FORCES

Forces and Their Effects – Test it!

Forces and Their Effects – Test it!

1. A cable car is used to take skiers to the top of a mountain.

a) The total mass of the skiers and the cable car is 7000 kg. The gravitational field strength is 10 N/g. Calculate the weight of the skiers and the cable car.

b) Once at the top, the skiers head back down the mountain on the skis. Explain why and how the skier’s kinetic energy changes.

2. A motorcyclist is driving down a road. The rider has two forces acting on them: 2100 N pushing her forward and 850 N resistant forces.

a) The mass of the motorbike and the rider together is 250 kg. Calculate the acceleration of the motorbike at this moment.

b) There are concerns over the number of motorcyclist accidents. Steel crash barriers are of particular concern as when a motorcyclist rides into one at high speed they can seriously hurt themselves. Polyurethane foam is used to cover the steel posts to reduce the risk. Using the idea of momentum explain how the foam can reduce the risk of injury.

3. A steel ball-bearing is dropped into a tube filled with oil.

a) Two forces act are acting on it: H is the upward force and G is the downwards force. What is the downward force G?

b) As the ball-bearing drops through the oil it decelerates at first and then starts to fall at a constant speed. Explain why using the forces H and G.

c) What is the name of the constant speed it reaches?

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ANSWERS

1. a) 7000 x 10 = 70000 newtons (N)

b) Their gravitational potential energy is transformed into kinetic energy and so their speed increases as they ski down the hill.

2. a) 1250 / 250 = 5

b) The foam decreases the rate of change in momentum. By increasing the time taken to stop the force is reduced on the rider.

3. a) Gravity

b) At first H is greater than G. As the speed of the ball-bearing increases the force G increase until both forces equal out and the speed of the ball-bearing becomes constant.

c) Terminal velocity