1) A horizontal force of 90 N is used to push a box across a horizontal floor. The frictional force on the box is 50 N. What is the gain in kinetic energy of the box when it is moved through a distance of 6.0 m?

2) An electric motor is required to haul a cage of mass 400 kg up a mine shaft through a vertical height of 1200 m in 2.0 minutes. What will be the electrical power required if the overall efficiency is 80%?

3) A car of mass 1000 kg first travels forwards at 25 m s^–1 and then backwards at 5 m s^–1.

What is the change in the kinetic energy of the car?

4) An object of mass 5.0 kg is carried a distance of 4.0 m across a room at a constant height  above the floor. What is the work done on the object?

5) The energy absorbed by a solar panel is used to charge a battery. During the day, the battery stores 1.6 J of energy each second. At night, the battery is used to light a 1.2 W lamp for 18 000 s.

What is the minimum time for which the battery must be charged during the day?