Assignment 6

REMEMBER - when doing a question which involves a calculation

a) Write down the equation you are using
b) Show your working out neatly
c) Dont forget the units on your answer

1. a man of mass 80 kg climbs stairs to a height of 30m. How much g.p.e. does he gain?  (take g = 9.8 N/kg)

2. a car of mass 300 kg is travelling at 20 m/s. Calculate its kinetic energy.

3. An electric motor does 12,000 J of work in 30 s.

a) Calculate its power.

b) if it uses 20,000 J of electrical energy in this time what is its efficiency?

4. A 3 kW electric kettle is used for a total of 2 hours in a week.

a) How many units (kWh) of electricity does it use?

b) if 1 unit costs 9p what is the cost of using the kettle?

5. A passenger in a car has a mass of 60 kg and is travelling at 30 m/s

a) How much momentum does she have?

b) If the car slows down suddenly in 0.2 s calculate the average force slowing the person down.

6. The door of a house has an area of 2 m² and a U value of 2.2 W/m²K

Calculate the rate of flow of heat through the door when the temperature difference either side of it is 18 ⁰C