Q13 of 101 Page 130

When an apple falls from a tree what happens to its gravitational potential energy just as it reaches the ground? After �t strikes the ground?

When apple falls from the tree, the gravitation potential energy keeps on decreasing as it is a function of height. It keeps on the decreasing until it strikes the ground where it is zero and remains unchanged for as long as height remains unaltered.


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11

In one of the exercises to strengthen the wrist and fingers, a person squeezes and releases a soft rubber ball. Is the work done on the ball positive, negative or zero during compression? During expansion?

 12

In tug of war, the team that exerts a larger tangential force on the ground wins. Consider the period in which a team is dragging the opposite team by applying a larger tangential force on the ground. List which of the following works are positive, which are negative and which are zero?

(a) work by the winning team on the losing team


(b) work by the losing team on the winning team


(c) work by the ground on the Winning team


(d) work by the ground on the losing team


(e) total external work on the two teams.


 14

When you push your bicycle up on an incline the potential energy of the bicycle and yourself increases. Where does this energy come from?

 15

The magnetic force on a charged particle is always perpendicular to its velocity. Can the magnetic force change the velocity of the particle? Speed of the particle?