Question

a) A bag is carried in from your car. How much work do you do on the bag? The distance from the car to the house is 10 m and the ground is flat.

b) A person is in a boat in the middle of a lake without a motor or oars. You have a box of balls in the boat. How do you get to shore, assuming the lake is frictionless? (Think conservation of momentum)

c) The same forces act for the same length of time on two different mass objects. Is the magnitude of the change in momentum of the lighter object greater than, less than, or equal to the magnitude of the change in momentum of the heavier object? Why or why not?

Answer 1

a) If the bag is carried horozontally from the car to the house then the force and displacement are perpendicular to each other. Hence the work done is zero.  ;

b) If a ball is thrown in a direction then the boat will move in opposite direction according to conservation of momentum. If the balls are thrown continuosly then the boat moves in opposite direction with increasing speed. Hence the boat reaches the shore.

c) If the same force acts for same time on the two objects then Ft is same. Ft is change in momentum. Hence the magnitude of change in momentum is same for both the bodies irrespective of their masses.