# Engineering Physics Questions and Answers – Friction and Motion

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

1. Three different objects of masses m1, m2 and m3 are allowed to fall from rest and from the same point O along three different frictionless paths. The speeds of the three different objects on reaching the ground will be in the ratio of ___________
a) m1:m2:m3
b) 1:1:1
c) 1/m1:1/m2:1/m3
d) m1:2m2:3m3

Explanation: v2-02=2gh
v=√2gh
This velocity does not depend on mass.

2. A truck and a car are moving with equal velocity. On applying brakes, both will stop after a certain distance, then?
a) Truck will cover less distance before stopping
b) Car will cover less distance before stopping
c) Both will cover equal distance
d) None of the mentioned

Explanation: Being lighter than a truck, the car has less kinetic energy. On applying brakes with the same force, the car will cover less distance before coming to rest.

3. If a ladder weighing 250N is placed against a smooth vertical wall having a coefficient of friction between it and floor 0.3, then what is the maximum force of friction available at the point of contact between the ladder and the floor?
a) 75N
b) 35N
c) 50N
d) 25N

Explanation: f = μR = μmg
f = 0.3×250 = 75N.

4. A body of mass 2kg begins to slide down a plane inclined at an angle of 45° with the horizontal. The force of friction will be?
a) 19.6sin 45°
b) 9.8sin 45°
c) 19.6cos 45°
d) 9.8cos 45°

Explanation: When the body just slides down on the inclined plane,
f = mgsinθ = 2×9.8sin 45°
f = 19.6sin 45°.

5. A person sitting in an open car moving at constant velocity throws a ball vertically into the air, the balls falls ____________
a) Exactly in the hand of the thrower
b) Outside the car
c) In the car ahead of the person
d) In the car behind the person

Explanation: Both the person and the ball share the horizontal velocity of the car. Hence the ball falls exactly in the hand of the thrower.

6. A stone of mass m tied to one end of a string of length l is rotated in a circle with the other end of the string as the centre. The speed of the stone is v. If the string breaks, the stone will ___________
a) Move towards the centre
b) Move away from the centre
c) Move along tangent
d) Stop

Explanation: When the string breaks, the centripetal force becomes zero. The stone moves along the tangent to the circular path. That is in the direction of velocity.

7. Two racing cars of masses m1 and m2 are moving in circle of radii r1 and r2 respectively. Heir speeds are such that each car makes a complete circle in same time t. The ratio of the angular speed of the first to the second car is ___________
a) 1:1
b) r1:r2
c) m1:m2
d) m1 m2:r1 r2

Explanation: w=2π/T
For both cars, period of revolution T is same, so their angular speed w is also same.

8. A man weighs 80kg. He stands on a weighing scale in a lift which is moving upwards with a uniform acceleration of 5m/s2. What would be the reading on the scale?
a) Zero
b) 400N
c) 800N
d) 1200N

Explanation: As the lift accelerates upward, the apparent weight,
R = m(g+a) = 80(10+5) = 1200N.

9. Consider a car moving along a straight horizontal road with a speed of 72km/h. If the coefficient of static friction between the tyres and the road is 0.5, the shortest distance in which the car can be stopped is? (g=10m/s2)
a) 30m
b) 40m
c) 72m
d) 20m

Explanation: Retardation, a = -μg = -0.5×10 = -5m/s2
u = 72km/h = 20m/s
As v2-u2=2as
s = 40m.

10. A boy of 50kg is standing in a lift moving down with an acceleration 9.8m/s2. The apparent weight of the boy is?
a) Zero
b) (50×9.8)N
c) 50N
d) 50/9.8N

Explanation: Apparent weight = m(g-a)
Apparent weight = 50(9.8-9.8) = 0.

Sanfoundry Global Education & Learning Series – Engineering Physics.

To practice all areas of Engineering Physics, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]