# Engineering Physics Questions and Answers – Acceleration due to Gravity

This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Acceleration due to Gravity”.

1. Can earth be regarded as a point object when describing its yearly journey around the sun?
a) Yes
b) No

Explanation: Earth can be regarded as a point object when describing its yearly journey around the sun because the size of the earth is much smaller than the distance from the sun.

2. Displacement can be greater than the distance travelled by an object.
a) True
b) False

Explanation: The displacement of an object can be either equal to or less than the distance travelled by the object. This is because displacement is the shortest distance between the initial and final positions of the object while distance travelled is the length of the actual path traversed by the object.

3. Under what condition is the average velocity equal to the instantaneous velocity?
a) Varying velocity
b) Varying speed
c) Constant velocity
d) Constant speed

Explanation: When a body moves with a constant velocity, its average velocity over any time interval is same as instantaneous velocity.

4. How is the speed related to the magnitude of velocity?
a) Greater
b) Lesser
c) Equal
d) Doesn’t vary

Explanation: Due to change in direction of motion, the length of the path traversed by a body is generally greater than the magnitude of its displacement. So the speed is greater than the magnitude of the velocity.

5. Two balls of different masses (one lighter and one heavier) are thrown vertically upward with same initial speed. Which one will rise to a greater height?
a) The lighter one
b) The heavier one
c) Neither
d) Both the balls

Explanation: Both he balls will rise to the same height. It is because, for a body moving with given initial velocity and acceleration, the distance covered by the body does not depend on the mass of the body.
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6. When rain falls vertically downwards, the front screen of a moving car gets wet while the back screen remains dry.
a) True
b) False

Explanation: When the rain is falling vertically downwards, the front screen of a moving car gets wet while back screen remains dry. This is because the rain strikes the car in the direction of relative velocity of rain with respect to the car.

7. Two trains A and B of length 400m each are moving on two parallel tracks with a uniform speed of 72km/h in the same direction, with A ahead of B. The driver of B decides to overtake A and accelerates by 1m/s. If after 50s, the guard of B just brushes past the driver of A, what is the original distance between them?
a) 50m
b) 150m
c) 125m
d) 1250m

Explanation: Let x be the distance between then driver of train A and the guard of train B. Initially, both trains are moving in the same direction with the same speed of 72km/h. So relative velocity of B with respect to A = vB-vA = 0. Hence the train B needs to cover a distance with a= 1m/s, t = 50 s, u = 0
s = ut + 1/2at2 = 1250m.

8. A player throws a ball upwards with an initial speed of 29.4m/s. What is the direction of acceleration during the upwards motion of the ball?
a) Upwards
b) Diagonal
c) Projectile motion
d) Vertically downwards

Explanation: The ball moves under the effect of gravity. The direction of acceleration due to gravity is always vertically downwards.

9. A particle in one dimensional motion with zero speed may have non-zero velocity.
a) True
b) False

Explanation: Speed is a magnitude of velocity and the magnitude of non-zero velocity cannot be zero.

10. For a particle in one dimensional motion, which of the following is true?
a) Zero speed at any instant may have zero acceleration at the instant
b) Zero speed may have non-zero velocity
c) Constant speed must have zero acceleration
d) Positive value of acceleration must be speeding up

Explanation: When a particle moves with a constant speed in the same direction, neither the magnitude nor the direction of velocity changes and so acceleration is zero. In case a particle rebounds instantly with the same speed, its acceleration will be infinite which is physically not possible.

11. A bullet fired into a fixed target loss half of its velocity after penetrating 3cm. How much further will it penetrate before coming to rest assuming that it faces constant resistance in motion?
a) 1.5cm
b) 1cm
c) 3cm
d) 2cm

Explanation: If u is initial velocity then v=u/2 s=3cm
As v2-u2=2as
a = -u2/8
Now v=0
Initial velocity=u/2
s=1cm
Thus the bullet will penetrate a further distance of 1cm before coming to rest.

12. From a building 2 balls A and B are thrown such that A is thrown upward and B is thrown downward. If vA and vB are their respective velocities on reaching the ground, then _____________
a) vB is greater than vA
b) vB = vA
c) vB is lesser than vA
d) Their velocities depend on their masses.

Explanation: Suppose the ball A is thrown upward with velocity u and ball B is thrown downward with same velocity u. After reaching the highest point the ball A comes back to its position with the same velocity in downward direction. As the 2 balls fall from the same position with the same velocity, both attain the same velocity on reaching the ground.

13. The displacement of the body is given to be proportional to the cube of time elapsed. The magnitude of acceleration of body is ____________
a) Increasing with time
b) Decreasing with time
c) Constant but not zero
d) Zero

Explanation: s=kt3
Velocity=ds/dt=3kt2
Acceleration=dv/dt=6kt
Clearly acceleration increases uniformly with time.

14. When a ball is thrown vertically upwards, at the maximum height ____________
a) The velocity is zero and therefore there is no acceleration acting in the particle
b) The acceleration is present and therefore the velocity is not zero
c) Acceleration depends on the velocity
d) Acceleration is independent of the velocity

Explanation: When a ball is thrown vertically upward, at the maximum height the acceleration becomes independent of the velocity.

15. Tom and Jerry are running forward at the same speed. They are following a rubber ball at a constant speed v as seen by the thrower. According to Sam, who’s standing on the ground, the speed of the ball is ____________
a) Same as v
b) Greater than v
c) Less than v
d) Zero

Explanation: As they are moving in the same direction, the relative velocity of the ball with respect to Tom or Jerry will be
vB=v+v(Tom or Jerry)
For Sam, the speed of the ball will be greater than v.

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