Question

A 75-kg person, starting from rest, sleds down a slide 40. m high hill reaching the bottom with a speed of 18 m/s. Calculate a) the PE at the top, b) the KE at the bottom of the hill, c) and finally, the thermal energy that was generated in the process.

Answer 1

a)

PE = mgh

Where:

PE = potential energy

m= mass = 75 kg

g= acceleration due to gravity = 9.8 m/s^2

h= hieght = 40 m

Replacing:

PE = 75 kg * 9.8 m/s^2 * 40m = 29,400 J

b)

KE = 1/2 m v^2

Where:

KE = kinetic energy

m= mass = 75 kg

v = speed = 18 m/s

Replacing:

KE = 1/2 * 75 kg * (18 m/s)^2 = 12,150 J

C) Thermal energy:

E2 - E1 = KE - PE = 12,150 - 29,400 J = -17,250 J = 17,250 J