Question Answers

Newton's Law

1. It is easier to pull a heavy load than to push it. Why?

When a heavy load is pushed away, force is applied against the gravitational force between the load and the pushing body. Hence more force is applied. But while pulling, the gravitational attraction force between the load and the pulling body reduces the applied force required to pull the load. Hence, it is easier to pull a heavy load than to push it.

2. A man drops his briefcase in an elevator but it does not fall to the floor. What can be concluded about the situation?

When the man drops his briefcase, the briefcase falls with the acceleration equal to the acceleration due to gravity. Since, the briefcase does not fall to the floor, the acceleration of floor or elevator should be equal to acceleration of the falling briefcase i. e, acceleration due to gravity. Hence, the elevator is free falling downward with acceleration equal to g.

3. A cricketer lowers his hands while catching balls why?

When a cricketer catches a ball, the moving ball stops and thus there is change in momentum of the ball. When he lowers his hands while catching, the time of impact for the same change of momentum is increased. So, the force applied on his hand is less and thus gets less injury.

4. In rain a scooter may slip on the turning of a road. Why?

When a scooter turns on a road, an outward force acts on the scooter away from the center of the turning. But, the frictional force between the tyre of the scooter and road makes the motion of the scooter possible. In rain the road is wet and thus frictional force is very less than the outward force and the scooter slips.

5. When a large heavy truck collides with a passenger car, the occupants of the car are more likely to be hurt than the truck driver. Why?

When a large heavy truck collides with a car, the truck applies an action force on the car. At the same time the car also applies a reaction force of equal magnitude to the truck but in opposite direction. Thus the same forces are applied on both the vehicles in opposite direction but the effect of the force is greater in the small object, car. Hence, the occupants of the car are more likely to be hurt than the truck driver.

6. Why does a heavy rifle not kick as strongly as a light rifle using the same cartridges?

When a bullet is fired, the rifle recoils with momentum equal and opposite to that of the bullet. When the rifle is heavy, mass would be higher which makes the recoil velocity less. For a light rifle the recoil velocity will be more. Hence the light rifle kicks strongly than the heavy rifle.

7. Why a man getting out of a moving bus must run in the same direction for a certain distance?

When a man gets out of a moving bus, his foot comes to rest but due to inertia of motion his upper body part is still in motion tending him to fall forward. So, to prevent from falling, he must run in the direction of bus for certain distance.

8. Explain why a coin placed on a cardboard covering a glass falls into the glass when the cardboard is pulled suddenly to one side?

When the cardboard is suddenly pulled, the coin placed on the cardboard still tends to be in its state of rest at the same position due to inertia of rest. But as the cardboard is removed, there is nothing to support the coin, it falls into the glass.

9. Why is kinetic friction less than the limiting friction?

The maximum value of static friction is the limiting friction. Initially, it requires more force to break the boundness between the two surfaces in contact. But once the surface is in motion, it requires less force to slide on the surface with the presence of inertia of motion. So, the force of friction when the surface is in motion i. e, kinetic friction is less than the limiting friction.

10. If a moving bullet striking a block of wood on a frictionless table embeds inside it what happens to the K. E. of the bullet?

When a moving bullet embeds inside a block of wood on a frictionless table, the K. E. of the bullet is transferred into the K. E. of the block and thus, the block moves with some velocity in the direction of motion of the bullet.

11. Why is it difficult to run fast on sand?

When we put our foot on sand, it is pressed down. Thus, the force exerted by our foot on the sand is less because the time of impact is large. Hence, we get less reaction force from the sand which makes us difficult to run fast.