Question

20 A 15 kg object rests at 10 m height.
a) Calculate its kinetic and potential energy.
b) It starts to fall, and at a given moment, its kinetic energy is 470 J. If you neglect friction with the air, what is its potential energy at that moment? How high is it?

Answer 1

Explanation:

a. Kinetic energy = 0 (as speed is zero and it is at a height).

Potential energy = mgh

= 15 x 9.8 x 10 = 1470 J

b. Using conservation of energy

Ki + Ui = Kf + Uf

0 + 1470 = 470 + Uf

Uf = 1000 J

we know that mgH = U

H = U /mg

H = 1000/15 × 9.8 = 6.80 m