G = 10 N/kg or 10 m/s2
A tennis ball of mass 0.2 kg drops from a height of 20 m. When it hits the ground, it bounces to a height of 14 m.

Describe what happens next
What was the Potential Energy (EP) of the ball before it fell?
What was the efficiency of the bounce?
How fast will Danielle be moving as she reaches the bottom of the hill?

a) , b) , c)

Explanation:

a) The initial potential energy is:

b) The efficiency of the bounce is:

c) The final speed of Danielle right before reaching the bottom of the hill is determined from the Principle of Energy Conservation:

chemical energy --> gravitational potential energy --> kinetic energy --> elastic potential energy --> gravitational potential energy

explanation:

when emma starts the hike, the chemical energy stored in her body is used to climb up the mountain, and so she gains gravitational potential energy (because at the end, she will be at a higher height h above the ground). then she goes bungee jumping: as she falls, this gravitational potential energy is converted into kinetic energy (because her speed increases as she falls down), until the point when the rope stretches, and she stops moving. at that moment, all the kinetic energy is converted into elastic potential energy due to the stretching of the rope. then, this energy is released because the rope returns to its natural length, and emma gains a small increase in altitude , so she gains some gravitational potential energy.