Answer:
B. the Big Bang
Explanation:
Answer:
When the early universe cooled enough for atoms to form, Nucleosynthesis began.
hope it helps!
A 0.009 kg bullet fired through a door enters at 803 m/s and leaves at 617 m/s. If the door material is known to exert an average resistive force of 5620 N on bullets of this type at usual speeds, find the thickness of the door.
Answer:
The thickness of the door is 0.4230 m
Explanation:
Given;
mass of bullet, m = 0.009 kg
initial velocity of the bullet, u = 803 m/s
final velocity of the bullet, v = 617 m/s
average resistive force of the door on the bullet, F = 5620 N
Apply Newton's second law of motion;
Force exerted by the door on the bullet = Force of the moving bullet
F = ma
where;
F is applied force
m is mass
a is acceleration
Also, Force exerted by the door on the bullet = Force of the moving bullet
[tex]F =ma, \ But \ a =\frac{dv}{dt} = \frac{u-v}{t} \\\\F = \frac{m(u-v)}{t}[/tex]
where;
v is the final velocity of the bullet
u is initial velocity of the bullet
t is time
We need to calculate the time spent by the bullet before it passes through the door.
[tex]t = \frac{m(u-v)}{F} \\\\t = \frac{0.009(803-617)}{5620} = 0.0002979 \ s[/tex]
Distance traveled by the bullet within this time period = thickness of the door
This distance is equivalent to the product of average velocity and time
[tex]S = (\frac{u+v}{2}) t[/tex]
where;
s is the distance traveled
[tex]S = (\frac{u+v}{2}) t\\\\S = (\frac{803+617}{2}) 0.0002979\\\\S = 0.4230 \ m[/tex]
Therefore, the thickness of the door is 0.4230 m
A steam engine takes in superheated steam at 270 °C and discharges condensed steam from its cylinder at 50 °C. The engine has an efficiency of 30%, and taken in 50 kJ from the hot steam per cycle. If a Carnot engine takes in the same amount of heat per cycle and operates at these temperatures, the work it can turn into is most likely to be:a) 15 kJ. b) 20 kJ. c) 10 kJ. d) 50 kJ.
Answer:
b) 20 kJ
Explanation:
Efficiency of carnot engine = (T₁ - T₂ ) / T₁ Where T₁ is temperature of hot source and T₂ is temperature of sink .
T₁ = 270 + 273 = 543K
T₂ = 50 + 273 = 323 K
Putting the given values of temperatures
efficiency = (543 - 323) / 543
= .405
heat input = 50 KJ
efficiency = output work / input heat energy
.405 = output work / 50
output work = 20.25 KJ.
= 20 KJ .
Mr.smith and his wife were trying to move their new chair. Mr. Smith pulls with a force of 30N while Mrs.Smith pushes with a force of 25N in the same direction. What is the net force?
Answer:
55N
Explanation:
30N + 25N = 55N
A plane electromagnetic wave varies sinusoidally at 90.0 MHz as it travels along the x direction. The peak value of the electric field is 200 V/m, and it is directed along the y direction. Find the wavelength, the period and the maximum value of the magnetic field. Write expressions in SI units for the space and time variations of the electric field and of the magnetic field. Include numerical values, and include subscripts to indicate coordinate directions. Find the average power per unit area that this wave propagates through space.
Answer:
Explanation:
frequency n = 90 x 10⁶ Hz .
time period T = 1 / n
= 1 / 90 x 10⁶
= 1.11 x 10⁻⁸ S.
wavelength = velocity of light / frequency
= 3 x 10⁸ / 90 x 10⁶
= 3.33 m
maximum value of the magnetic field. ( B₀ )
E₀ / B₀ = c where E₀ and B₀ are maximum electric and magnetic field .
E₀ / c= B₀
200/ 3 x 10⁸
= 66.67 x 10⁻⁸ T .
expressions in SI units for the space and time variations of the electric field
[tex]E=E_{0y}sin(2\pi nt - \frac{2\pi x}{\lambda} )[/tex]
[tex]E=200sin(180\times 10^6\pi t - \frac{2\pi x}{\lambda} )[/tex] N/C
[tex]B=B_{0z}sin(2\pi nt - \frac{2\pi x}{\lambda} )[/tex]
[tex]B=66.67\times 10^{-8}sin(180\times 10^6\pi t - \frac{2\pi x}{\lambda} )[/tex] T
A possible means for making an airplane invisible to radar is to coat the plane with an antireflective polymer. If radar waves have a wavelength of 2.92 cm and the index of refraction of the polymer is n = 1.30, how thick (in cm) would you make the coating? (Assume that the index of refraction of the plane is higher than that of the coating. Also assume that the radar waves are normal to the surface of the coating. Give the minimum thickness that would make the airplane invisible to radar.)
Answer:
The thickness is [tex]t = 0.5615 \ cm[/tex]
Explanation:
From the question we are told that
The wavelength of the of the rader waves is [tex]\lambda = 2.92 \ cm[/tex]
The index of refraction of the polymer is [tex]n = 1.30[/tex]
The thickness is mathematically represented as
[tex]t = \frac{\lambda }{4 n }[/tex]
Substituting values
[tex]t = \frac{2.92}{4 * 1.30 }[/tex]
[tex]t = 0.5615 \ cm[/tex]
Which is the correct representation of the right-hand rule for a current flowing to the right?
Answer:
The third image
Explanation:
The one with the thumb pointing to the right
Answer:
3, correct on Edge 2020
Help ill give you brainliest !!!
Answer:
1. B
2. A
3. C
4. B
5. A
6. Muscular strength is different than muscular endurance because of the fact that muscular strength is the amount of force that can be exerted in one instance. Muscular endurance is how long that you can exert that force without being completely exhausted.
7. Some benefits to strength training is the increase in muscular endurance. There is also the benefit of better muscular strength.
Explanation:
A rectangular painting measures 1.0 m tall along the y' axis and 3.0 m wide along the
x' axis. The painting is hung on the side wall of a spaceship which is moving passed
the Earth at a speed of 0.9c. Assume that the spaceship is moving along the (x, x')
direction.
a) What are the dimensions of the picture according to the captain of the
spaceship?
b) What are the dimensions of the picture as seen by an observer on the Earth?
Answer:
a) 1 m tall, 3 m wide
b) 1 m tall, 1.31 m wide
Explanation:
According to the captain of the spaceship, the dimensions of the picture is the same i.e 1.0 m tall along the y' axis and 3.0 m wide along the x' axis.
b) The dimensions of the picture as seen by an observer on the Earth along the y axis will remain the same, 1.0 m tall, for the direction of the y axis is perpendicular to the spaceship movement.
The dimensions of the picture as seen by an observer on the Earth along the x axis will reduce if we are to go by the Lorentz contraction:
L(x) = L(x)' * √[1 - (v²/c²)]
where
L(x)' = the dimensions of the picture along the x axis on the spaceship,
v² = the speed of the spaceship and c² = the speed of light in the vacuum.
On substituting, we have
L(x) = 3 * √[1 - (0.81c²/c²)]
L(x) = 1.31 m
A pendulum is swinging back and forth with no non-conservative forces acting on it. At the highest points of its trajectory, the kinetic energy of the pendulum bob is instantaneously equal to zero joules. At the lowest point of its trajectory, the potential energy is instantaneously equal to zero joules. Which one of the following expressions describes the kinetic and potential energies at the point mid-way between to the highest and lowest points?
A. K = 0, U = Umax
B. K = U
C. K < U
D. K > U
E. U = 0, K = Kmax
Answer:
K = U ( b )
Explanation:
The expression that describes the kinetic and potential energies at the point mid-way between to the highest and lowest points is K = U
this is because at the midpoint between the highest point and the lowest point the height is expressed as( h/2) therefore potential energy at that point is expressed as m*g*h/2 therefore the remaining energy at this point will be considered the kinetic energy which will be = m*g*h/2 as well hence at midpoint Kinetic energy = potential energy
Who is having a hallucination?
O
A. Dominique, who doesn't know who she is anymore
O
B. Jasmine, who believes that she is a millionaire and is really a
princess
O
C. Damion, who suffers a concussion after a football game and has
memory problems
O
D. Terrance, who suffers from schizophrenia and sees faces looking
at him in the wall
Answer:
D. Terrance
Explanation:
This is because he is seeing things that aren't there.
Dominique has amnesia (useless it's just like an existential crisis)
Jasmine is having delusions? but she's not hallucinating.
Damion has I guess temporary amnesia? Maybe brain damage? but not hallucinations.
Consider a circular vertical loop-the-loop on a roller coaster. A car coasts without power around the loop. Determine the difference between the normal force exerted by the car on a passenger with a mass of mm at the top of the loop and the normal force exerted by the car on her at the bottom of the loop. Express your answer in terms of mmm and the acceleration due to gravity ggg.
Answer:
Explanation:
Let v₁ and v₂ be velocities at lowest and topmost position . Let r be the radius of the circle .
Let N₁ and N₂ be the normal reaction force .
At the top position
centripetal force = N₂ + mg ; so
N₂ + mg = m v₂² / r
At the bottom position
centripetal force = N₁ - mg ; so
N₁ - mg = m v₁² / r
subtracting these two equations
N₁ - mg - N₂ - mg = m v₁² / r - m v₂² / r
N₁ - N₂ - 2mg = 1/r (m v₁² - m v₂² )
N₁ - N₂ - 2mg = 1/r x mg x 2r ( loss of potential energy = gain of kinetic energy )
N₁ - N₂ = 2mg + 2mg
= 4 mg .
A particle is projected at an angle 60 degrees to the horizontal with a speed of 20m/s. (i) calculate total time of flight of the particle. (i) speed of the particle at its maximum height
Answer:
Time of flight=3.5 seconds
Speed at maximum height is 0
Explanation:
Φ=60°
initial velocity=u=20m/s
Acceleration due to gravity=g=9.8 m/s^2
Total time of flight=T
Final speed=v
question 1:
T=(2 x u x sinΦ)/g
T=(2 x 20 x sin60)/9.8
T=(2 x 20 x 0.8660)/9.8
T=34.64/9.8
T=3.5 seconds
Question 2
Speed at maximum height is 0
A brick is dropped from a high scaffold.
a. How far does the brick fall during this time?
Answer:
a: after 1 seconds it will have fallen 0.2452
after 2 seconds it will have fallen 0.981
after 3 seconds it will have fallen 2.2072
after 4 seconds it will have fallen 3.924
Explanation:
the formula for acceleration due to gravity is (ignoring friction I think)
g = G*M/R^2
earths gravitational constant is about 9.807
g = 9.807*M/R^2
The average weight of a brick is 5 pounds and I'm going to say it's 10 feet off the ground.
g = 9.807*5/10^2. g = 0.4905 so every second the brick will go 0.4905 fps faster. (fps means feet per second.)
after 1 seconds it will have fallen 0.2452
after 2 seconds it will have fallen 0.981
after 3 seconds it will have fallen 2.2072
after 4 seconds it will have fallen 3.924
A 200.0 g block rests on a frictionless, horizontal surface. It is pressed against a horizontal spring with spring constant 4500.0 N/m (assume that the spring is massless). The block is held in position such that the spring is compressed 4.00 cm shorter than its undisturbed length. The block is suddenly released and allowed to slide away on the frictionless surface. Find the speed the block will be traveling when it leaves the spring.
Answer:
6 m/s
Explanation:
Given that :
mass of the block m = 200.0 g = 200 × 10⁻³ kg
the horizontal spring constant k = 4500.0 N/m
position of the block (distance x) = 4.00 cm = 0.04 m
To determine the speed the block will be traveling when it leaves the spring; we applying the work done on the spring as it is stretched (or compressed) with the kinetic energy.
i.e [tex]\frac{1}{2} kx^2 = \frac{1}{2} mv^2[/tex]
[tex]kx^2 = mv^2[/tex]
[tex]4500* 0.04^2 = 200*10^{-3} *v^2[/tex]
[tex]7.2 =200*10^{-3}*v^{2}[/tex]
[tex]v^{2} =\frac{7.2}{200*10^{-3}}[/tex]
[tex]v =\sqrt{\frac{7.2}{200*10^{-3}}}[/tex]
v = 6 m/s
Hence,the speed the block will be traveling when it leaves the spring is 6 m/s
Two forces are applied on a body. One produces a force of 480-N directly forward while the other gives a 513-N force at 32.4-degrees above the forward direction .Find the magnitude and direction(relative to forward direction of the resultant force that these forces exert on the body)
Answer:
F = (913.14 , 274.87 )
|F| = 953.61 direction 16.71°
Explanation:
To calculate the resultant force you take into account both x and y component of the implied forces:
[tex]\Sigma F_x=480N+513Ncos(32.4\°)=913.14N\\\\\Sigma F_y=513sin(32.4\°)=274.87N[/tex]
Thus, the net force over the body is:
[tex]F=(913.14N)\hat{i}+(274.87N)\hat{j}[/tex]
Next, you calculate the magnitude of the force:
[tex]F=\sqrt{(913.14N)+(274.87N)^2}=953.61N[/tex]
and the direction is:
[tex]\theta=tan^{-1}(\frac{274.14N}{913.14N})=16.71\°[/tex]
Eclipses of the sun and moon are best explained by which of the following?
The irregular shape of the orbits of Earth and the moon
The rotation of Earth and the moon on their axis
The revolution of Earth and the moon around the sun
The different chemical compositions of the sun and the moon
Answer:
Eclipses of the Sun and Moon are best explained by the revolution of Earth and the Moon around the Sun.
Explanation:
An eclipse is the covering of a star by another celestial body. In everyday language, an eclipse usually means a solar or lunar eclipse.
When the sun, moon and earth are aligned (in this order), the sun is covered by the moon when viewed from a place on earth. The sunlight will then no longer reach the earth. In other words, part of the earth has been eclipsed by the moon. This is referred to as a solar eclipse.
If the earth is between the sun and the moon, and thereby prevents sunlight from reaching the moon, then there is a lunar eclipse. After all, seen from the moon, the earth covers the sun. The moon is then eclipsed by the earth.
Dual Nature of Light
Assignment
Active
Explaining the Nature of Light
Why do scientists believe that light is made of streams of
particles?
Block A, with a mass of 4 kg, is moving with a speed of 2 m/s while Block B, with a mass of 8.4 kg, is moving in the opposite direction with a speed of 6.1 m/s. The center of mass of the two block system is moving with a velocity of ____ m/s. Round your answer to the nearest tenth. Assume Block A is moving in the positive direction.
Answer:
The center of mass move with the velocity of -3.487 m/s.
Explanation:
Given values of block A.
Mass of block A, (M1) = 4 kg
Speed of block A, (V1) = 2 m/s
Given values of block B.
Mass of block B, (M2) = 8.4 kg
Speed of block B, (V2) = -6.1 m/s
Below is the formula to find the velocity of center of mass.
[tex]Velocity = \frac{M1V1 + M2V2}{M1 + M2} \\[/tex]
[tex]= \frac{4 \times 2 + 8.4 \times (-6.1) }{4 + 8.4} \\[/tex]
[tex]= \frac{- 43.24}{12.4}\\[/tex]
[tex]= - 3.487 m/s[/tex]
Which of the following is not true about of the use of MRI in medicine?
1) It produces no negative side-effects on the human body
2) It produces high resolution images of soft tissues
3) It is very cheap
4) It requires very strong magnetic fields
Answer:
3) False. It is expensive since it requires sophisticated equipment and very low temperatures
Explanation:
Nuclear magnetic resonance imaging measurements consist of magnetic resonance imaging to analyze tissues by the transition of the unpaired electron at carbon 13, giving information on the structure and composition of tissues. This information is processed in computers and transformed into images.
So the physical measurement is the MRN
Now we can analyze the statements in the problem
1) True by itself a magnetic measurement is non-invasive
2) True. Measuring carbon transitions has information about the soft tissue of the body
3) False. It is expensive since it requires sophisticated equipment and very low temperatures
4) Right. The applied magnetic field is high to be able to induce carbon transaction
A ball with a mass of 4 kg is initially traveling at 2 m/s and has a 5 N force applied for 3 s. What is the initial momentum of the ball?
Answer:
The initial momentum of the ball is 8 kg-m/s.
Explanation:
Given that,
Mass of the ball is 4 kg
Initial speed of the ball is 2 m/s
Force applied to the ball is 5 N for 3 seconds
It is required to find the initial momentum of the ball. Initial momentum means that the product of mass and initial velocity of the ball. It is given as :
[tex]p_i=mu\\\\p_i=4\ kg\times 2\ m/s\\\\p_i=8\ kg-m/s[/tex]
So, the initial momentum of the ball is 8 kg-m/s.
water is pumped from a stream at the rate of 90kg every 30s and sprayed into a farm at a velocity of 15m/s. Calculate the power of the pump.
Answer:
340 W
Explanation:
Power = change in energy / change in time
P = ΔKE / Δt
P = ½ mv² / Δt
P = ½ (90 kg) (15 m/s)² / (30 s)
P = 337.5 W
Rounded to 2 significant figures, the power is 340 W.
The friends now feel prepared for a homework problem. Consider a cylinder initially filled with 9.30 10-4 m3 of ideal gas at atmospheric pressure. An external force is applied to slowly compress the gas at constant temperature to 1/6 of its initial volume. Calculate the work that is done. Note that atmospheric pressure is 1.013 105 Pa
Answer:
Explanation:
Initial volume of gas V₁ = 9.30 x 10⁻⁴ m³
final volume V₂ = 1 / 6 x 9.30 x 10⁻⁴
= 1.55 x 10⁻⁴ m³
Atmospheric pressure P = 1.013 x 10⁵ Pa .
temperature T .
PV = n RT
nRT = 1.013 x 10⁵ x 9.3 x 10⁻⁴
= 94.21
work done in isothermal process
= 2.303 nRT log V₁ / V₂
= 2.303 x 94.21 log 6
= 168.83 J .
It takes four hydrogen nuclei to create one helium nucleus in the proton–proton chain, which is the main energy source of the Sun. If a single hydrogen nucleus has a mass of 1.6726×10−27 kg and a single helium nucleus has a mass of 6.6447×10−27 kg , how much mass is converted into energy to create three helium nuclei?
Answer:
0.1371 * 10 ^ -27 kg
Explanation:
From the question number of hydrogen nuclei used to form 3 Helium nuclei = 12 ( 4 * 3 )
mass of the 12 hydrogen nuclei = 12 *( 1.6726 *10^-27) = 20.0712 * 10 ^-27
mass of single helium = 6.6447 * 10 ^-27 kg
therefore the mass of the 3 helium = 3 *( 6.6447 *10 ^-27) = 19.9341 * 10 ^-27 kg
The mass difference between the hydrogen and the helium used
= (20.0712 * 10^ -27) - (19.9341 * 10 ^-27) = 0.1371 * 10 ^ -27 kg
therefore 0.1371 * 10^-27 kg is converted into energy to create the three helium nuclei
A speaker system is plugged into a 100v socket and 2.5 a of current runs through. Find the power of the system
Answer:
250 Watts
Explanation:
Recall that the formula relating power, current and voltage is
P = IV, where,
P = power (we are asked to find this)
I = 2.5 A
V = 100 V
substituting the above values into the equation:
P = IV
= (2.5)(100)
= 250 Watts
Modified Newtonian dynamics(MoND)proposes that, for small accelerations, Newton’s second law, F = ma, approaches the form F = ma2/a0, where a0 is a constant.
(a) (10 points) Show how such a modified version of Newton’s second law can lead to flat rotation curves, without the need for dark matter.
(b) (10 points) Alternatively, propose a new law of gravitation to replace F = GMm/r2 at distances greater than some characteristic scale r0 so that again, you can explain the observed flat rotation curved of galaxies without dark matter.
Answer:
Explanation:
The two pictures attached here shows the solution to the two questions from the problem. thank you and I hope it helps you
what do hydroelectric plants use to generate electrical energy?
Answer:
A. falling water
Explanation:
I got it right on Edgenuity. Good luck on your quiz.
In hydroelectric plants, water falls on turbine and makes it rotate. In generator, this mechanical energy transforms into electrical energy.
What is hydroelectric power?Hydroelectric power is generated by turbines that turn the potential energy of falling or swiftly flowing water into mechanical energy, which is then used to power generators. The most popular renewable energy source in the early 21st century was hydroelectricity, which in 2019 accounted for more than 18% of the world's total power producing capacity.
Water is gathered or stored at a higher elevation during the production of hydroelectric power and then transported through substantial pipes or tunnels (penstocks) to a lower elevation; the difference between these two elevations is referred to as the head. The falling water turns turbines as it nears the bottom of the pipelines. In turn, the turbines power generators, which transfer the mechanical energy of the turbines into electricity.
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You are designing an optical fiber scope for directing light into a confined area. You want to keep light within the fiber. Based on the specifications, you know that the greatest angle that the light will make with the horizontal is no greater than 25⁰. Assuming you will be using the scope in the body which has the same index of refraction of water (n = 1.33). What is the minimum index of refraction n2 required for the design to be functional?
Answer:
Explanation:
For entry of light into tube of unknown refractive index
sin ( 90 - 25 ) / sinr = μ , μ is the refractive index of the tube , r is angle of refraction in the medium of tube
r = 90 - C where C is critical angle between μ and body medium in which tube will be inserted.
sin ( 90 - 25 ) / sin( 90 - C) = μ
sin65 / cos C = μ
sinC = 1.33 / μ , where 1.33 is the refractive index of body liquid.
From these equations
sin65 / cos C = 1.33 / sinC
TanC = 1.33 / sin65
TanC = 1.33 / .9063
TanC = 1.4675
C= 56°
sinC = 1.33 / μ
μ = 1.33 / sinC
= 1.33 / sin56
= 1.33 / .829
μ = 1.6 Ans
In this circuit the battery provides 3 V, the resistance R1 is 7 Ω, and R2 is 5 Ω. What is the current through resistor R2? Give your answer in units of Amps. An Amp is 1 Coulomb of charge flowing through a cross-sectional area of the wire per second - that's a lot of charge per second and will warm up a typical wire quite a bit! Most devices have circuits with larger resistors - kLaTeX: \OmegaΩ (103 LaTeX: \OmegaΩ) and MLaTeX: \OmegaΩ (106 LaTeX: \OmegaΩ) are common.
Answer:
The current pass the [tex]R_2[/tex] is [tex]I = 0.25 A[/tex]
Explanation:
The diagram for this question is shown on the first uploaded image
From the question we are told that
The voltage is [tex]V = 3V[/tex]
The first resistance is [tex]R_1 = 7 \Omega[/tex]
The second resistance is [tex]R_2 = 5 \Omega[/tex]
Since the resistors are connected in series their equivalent resistance is
[tex]R_{eq} = R_1 +R_2[/tex]
Substituting values
[tex]R_{eq} = 7 + 5[/tex]
[tex]R_{eq} = 12 \Omega[/tex]
Since the resistance are connected in serie the current passing through the circuit is the same current passing through [tex]R_2[/tex] which is mathematically evaluated as
[tex]I = \frac{V}{R_{eq}}[/tex]
Substituting values
[tex]I = \frac{3}{12}[/tex]
[tex]I = 0.25 A[/tex]
Derive the equation relating the total charge Q that flows through a search coil (Conceptual Example 29.3) to the magnetic-field magnitude B. The search coil has N turns, each with area A, and the flux through the coil is decreased from its initial maximum value to zero in a time Δt. The resistance of the coil is R, and the total charge is Q=IΔt, where I is the average current induced by the change in flux.
Answer:
Q= NBA/R
Explanation:
Check attachment for derivation
The equation relating the total charge, magnitude, turns, time will be "[tex]\frac{NBA}{R}[/tex]".
Magnetic fieldAccording to the question,
Resistance = R
Total charge = Q
Current = I
Number of turns = N
Time = Δt
and,
Q = IΔt ...(equation 1)
We know the flux,
→ [tex]\Phi[/tex] = NBA
Emf induced,
ε = [tex]\frac{- \Delta \Phi}{\Delta t}[/tex]
Δ[tex]\Phi[/tex] = [tex]\Phi_2 - \Phi_1[/tex]
then,
ε = [tex]\frac{NBA}{\Delta t}[/tex]
As we know, Voltage (V) = iR
then, ε = [tex]\frac{NBA}{\Delta t}[/tex] = iR
i = [tex]\frac{NBA}{R \Delta t}[/tex]
Hence, by applying the values in "equation 1"
→ Q = iΔt
= [tex]\frac{NBA}{R \Delta t}[/tex] × Δt
= [tex]\frac{NBA}{R}[/tex]
Thus the response above is correct.
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Which of the following statements are true? a. Kinematics is the science that studies forces and motion of particles and bodies. b. Speed is a vector quantity. c. The units of velocity are length divided by time. d. The term deceleration is commonly used to describe a negative acceleration.
Answer:
true. b, c and d
Explanation:
Let's review each statement separately
a) False. The kinematics studies the position, speed and acceleration of the bodies, but not what causes these changes
b) True. Velocity is the displacement between time, displacement is a vector, and time is a scalar, so the division between them gives a vector
c) True. speed is the displacement that is a length between time, so its unit is length / time
d) true desaceleration = - aceleration
