A ball, of mass 0.125 kg, is thrown so that its initial speed is 12 \displaystyle \text{m}{{\text{s}}^{-1}}. As the ball moves upwards its speed decreases to 4 \displaystyle \text{m}{{\text{s}}^{-1}} when it is at its maximum height.

a) Calculate the initial kinetic energy of the ball.

b) Calculate the minimum kinetic energy of the ball.

c) Calculate the potential energy of the ball at its maximum height.

Answer a

Answer b

Answer c

Solution a

Solution b

Solution c

Exercise 17.4

A brick, of mass 2 kg, is allowed to fall from rest at a height of 3.2 m. Find the kinetic energy and speed of the brick when it hits the ground;

a) assuming that no resistance forces act on the brick as it falls,

b) assuming that a constant resistance force of magnitude 10 N acts on the brick.

Answer a

Answer b

Solution a

Solution b

Exercise 17.5

A rock, which has mass 3 kg, is thrown from a bridge over a river at speed of 3 \displaystyle \text{m}{{\text{s}}^{-1}}. When it hits the water, it is moving at a speed of 15 \displaystyle \text{m}{{\text{s}}^{-1}}.

a) Find the kinetic energy gained as the rock falls.

b) Find the potential energy lost as the rock falls.

c) Find the height of the bridge above the river.

Answer a

Answer b

Answer c

Solution a

Solution b