The speed in meters/second of a ball dropped from height h meters is given by the function v = √20h. Its kinetic energy in joules (J) is given by the function T = 2v^2. What is the ball's kinetic energy if it is dropped from a height of 3 meters?
(Hint: First find speed and then find kinetic energy.)

Question

The speed in meters/second of a ball dropped from height h meters is given by the function v = √20h. Its kinetic energy in joules (J) is given by the function T = 2v^2. What is the ball's kinetic energy if it is dropped from a height of 3 meters?
(Hint: First find speed and then find kinetic energy.)

anonymous · Answer

120 joules

60 joules

20 joules

80 joules

matt101 · Answer

You can find speed then kinetic energy...or finish the question faster and with easier numbers by plugging the equation for speed into the equation for kinetic energy:

$$v=\sqrt{20h} \space \space \space (1)$$$$T=2v^2 \space \space \space \space \space \space (2)$$
Subbing (1) into (2) gives you:
$$T=2 (\sqrt{20h})^2=2(20h)=40h$$
If your starting height is 3 m, it's kinetic energy is T=40*3=120 J.