1. How much work is required to lift a 4kg object 3m high?
2. When a car stops, 60 000 J of work is done by the brakes
in a time of 6s. Calculate the power of the brakes.
3. A crane lifts a 90 kg mass a height of 12 m. Calculate the
gravitational potential energy gained by the mass. Use
g = 9.8 N/kg.
4. Determine the kinetic energy of a 750-kg roller coaster
car that is moving with a speed of 20.2 m/s.

Ahair dryer is basically a duct in which a few layers of electric resistors are placed. a small fan pulls the air in and forces it through the resistors where it is heated. air enters a 1200 w hair dryer at 100 kpa and 22°c and leaves at 47°c. the cross-sectional area of the hair dryer at the exit is 60 cm2. neglecting the power consumed by the fan and the heat losses through the walls of the hair dryer, determine (a) the volume flow rate of air at the inlet and (b) the velocity of the air at the exit.