A father and son pushed their car to bring it to the side of road as it had stalled in the middle of the road. They experienced that although they had to push with all their might initially to move the car, the push required to keep the car rolling was smaller, once the car started rolling. Explain.

A one-ton car moves with a constant velocity of 15 ms^(–1) on a rough horizontal road. The total resistance to the motion of the car is 12% of the weight of the car. The power required to keep the car moving with the same constant velocity of 15ms^(–1) is [Take g=10ms^(-2) ]

A car is moving at a constant speed of 40 km/h along a straight road which heads towards a large vertical wall and makes a sharp 90^0 turn by the side of the wall. A fly flyingat constant speed of 100 km/h, starts from the wall towrds the car t an instant when the car is 20 km away,flies until it reaches the glasspane of the car and returns to teh wll at teh same speed. It continues to fly between the car and teh wall time the car makes the 90^0 turn. a. What is the total distance the fly has travelled during the period?b. How many trips has it made between the car and the wall?

a. A rail road flat car of mass M can roll without friction along a straight horizontal track . Initially, a man of mass m is standing on the car which is moving to the right with speed v_(0) . What is the change in velocity of the car if the man runs to the left so that his speed relative to the car is v_(rel) just before he jumps off at the left end? b. If there are n men each of mass m on the car, should they all run and jump off together or should they run and jump one by one in order to give a greater velocity to the car?