Engineering Physics Problems focuses on “Friction and Forces – 2”.
1. A body in linear motion can never be in equilibrium.
a) True
b) False
Answer: b
Clarification: A body in linear motion can be in equilibrium provided that the vector sum of two forces acting upon the body is zero.
2. A man jumping out of a moving train ___________
a) Lands on the ground
b) Falls with his head forward
c) Will start rolling on the ground
d) Falls with this head backward
Answer: b
Clarification: As the man jumps out of a moving train, his feet suddenly come to rest on touching the ground while the upper part of his body continues to move forward. That is why he falls with his head forward. In order to save himself, he should run some distance in the forward direction.
3. A stone, when thrown on a glass window, smashes the windowpane to pieces, but a bullet from the gun passes through making a clean hole. Why?
a) Due to the large size of the stone
b) Depends on the material of the window
c) Because of the force
d) Because of the small speed of the stone
Answer: d
Clarification: Because of the small speed, the stone remains in contact with the windowpane for a longer period. It transfers its motion to the pane and breaks it into pieces. But the particles of windowpane near the hole are unable to share the fast motion of the bullet and so remain undisturbed.
4. An astronaut is suddenly thrown out of his small spaceship accelerating in interstellar space at a constant rate of 100/s2. What is the acceleration of the astronaut the instant after he is outside the spaceship? Assuming there are no nearby stars.
a) 200m/s2
b) 100 m/s2
c) Zero
d) 400 m/s2
Answer: c
Clarification: The moment he gets out of the ship, there is no external force on him. By the law of motion, the acceleration of the astronaut is zero.
5. A soda-water bottle is falling freely. The bubbles of the gas rise in the water of the bottle.
a) True
b) False
Answer: b
Clarification: The water in the freely falling bottle is in the state of weightlessness. Consequently, the pressure in water does not increase with depth. No upthrust acts on the bubbles and they do not rise.
6. A bird is sitting on the floor of a wire cage and the cage is in the hand of a boy. The bird starts flying in the cage. The boy will ___________
a) Also experience the flying feel
b) Will not feel anything different
c) Feel the weight of the cage has become lighter
d) Feel no change in weight of the cage
Answer: c
Clarification: The air inside the wire cage is in free contact with the atmospheric air. When the bird starts flying inside the cage, the weight of the bird is no more experienced and the cage will appear lighter than before.
7. When a man jumps down for a height of several storeys into a stretched tarpaulin, he receives no injury.
a) True
b) False
Answer: a
Clarification: When the man jumps, the tarpaulin gets depressed at the place of impact. This increases the time of impact. As a result, the tarpaulin exerts a very small force on the man, and he receives no injury.
8. The fuel in the vehicle can be saved by ___________
a) Not using vehicle often
b) Mixing water with fuel
c) Cleaning the vehicle
d) Properly inflating the tyres
Answer: d
Clarification: When the tyres are properly inflated, the area of contact between the tyre and the ground is reduced. This reduces rolling friction. Consequently, the automobile covers greater distance for the same quantity of fuel consumed.
9. Which of the brakes are effective on a bicycle?
a) Small ones
b) Bigger ones
c) Both small and big
d) Neither small nor big
Answer: c
Clarification: Action of brakes is based on friction. But the friction is independent of the area of surfaces in contact so long as the normal reaction remains the same, Hence, larger size brakes and normal size brakes will be equally effective if the material of brakes remains unchanged.
10. It is difficult to put a cycle into motion than to maintain the motion because of ___________
a) Limiting friction
b) Kinetic friction
c) Rolling friction
d) Static friction
Answer: a
Clarification: To put a cycle into motion, one needs to overcome limiting friction while maintaining its motion, one needs to overcome kinetic friction. Limiting friction is greater than kinetic friction. So it is difficult to put a cycle into motion than to maintain its motion.