# Engineering Physics Questions and Answers – Motion and Mechanics

This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Motion and Mechanics”.

1. Rest and motion are relative terms.
a) True
b) False

Explanation: A passenger sitting in a train is in rest with respect to his other passengers but is in motion with respect to the things outside the train. Thus, an object maybe at rest with respect to one object and, at the same time, in motion with respect to another object. Hence rest and motion are relative terms.

2. A train is under a journey of several hundred kilometers. How can it be regarded?
a) An object in motion
b) An object under rest
c) An object under absolute motion
d) A point object

Explanation: If the position of an object changes by distances much greater than its own size in a reasonable time, then the object maybe regarded as a point object.

3. A car is moving along a zigzag path on a level road. This is an example for which of the following?
a) Point object
b) Two dimensional motion
c) Three dimensional motion
d) One dimensional motion

Explanation: The motion of an object is said to be two dimensional if only two of the three coordinates specifying its position changes with time. Hence a car moving in a zigzag path on a level road is an example for two dimensional motions.

4. Which of the following can be regarded as an example for three dimensional motions?
a) Motion of planets around the sun
b) Motion of a train along a straight track
c) Motion of a free falling body
d) A kite flying on a windy day

Explanation: The motion of an object is said to be three dimensional if all the three coordinates specifying the position changes with respect time. Thus kite flying on a windy day is an example for three dimensional motions.

5. Displacement is a scalar quantity.
a) True
b) False

Explanation: Displacement is the change in a potion of an object in a fixed direction. It has both magnitude and direction. Thus displacement is a vector quantity.
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6. A body travels from A to B at 40m/s and from B to A at 60m/s. Calculate the average speed.
a) 0
b) 48m/s
c) 240m/s
d) 3.5m/s

Explanation: Total time taken by the body to travel from A to B and then from B to A,
t1+t2 = AB/40 + AB/60 = AB/24 s
Total distance covered = AB + BA = 2AB
Average speed = 2AB/(t1+t2) = 48m/s.

7. On a 60km track travels the first 30km with a uniform speed of 30km/h. How fast must the train travel the next 30km so as to average 40km.h for the entire trip?
a) 60km.h
b) 90km/h
c) 120km/h
d) 30km/h

Explanation: vav = (2v1 v2)/(v1+v2)
40 = (2×30×v2)/(30+v2)
v2 = 60km/h.

8. What is the acceleration of a bus approaching a bus stop?
a) Uniform acceleration
b) Instantaneous acceleration
c) Average acceleration
d) Negative acceleration

Explanation: If the velocity of an object decreases with time, its acceleration is negative. When a bus approaches its stop, its acceleration decreases, hence it has negative acceleration.

9. A jet plane starts from rest with an acceleration of 3m/s2 and makes a run for 35s before taking off. What is the minimum length of the runway?
a) 105 m
b) 1837.5 m
c) 2451 m
d) 1204 m

Explanation: Minimum length of the driveway is given by s = ut + 1/2 at2 = 0 + 1/2 × 3 × 35 × 35 = 1837.5 m.

10. A driver takes 0.20 s to apply the brakes after he sees a need for it. This is called the reaction time of the driver. If he is driving at a speed of 54km/h and the brakes cause a deceleration of 6.0m/s2, find the distance travelled by the car after he sees the need to put the brakes.
a) 18.75m
b) 225 m
c) 21.5 m
d) 12 m

Explanation: Distance covered in 0.20s = 15 × 0.20 = 3 m
For motion with deceleration:
U = 15m/s v = 0 a = -6 m/s2
As v2 – u2 = 2as
s = 18.75 m
Total distance travelled = 3.0 + 18.75 = 21.75 m.

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