A book falls off a desk. The book has a mass of 1.2 kg and was at a height of 0.9 m. How much mechanical energy does the book have just before it hits the ground? (Assume there is no air resistance.)

Question

anonymous · Answer

mgh

anonymous · Answer

Gravitational potential energy is
$$PE = m  g  h$$
m is mass (1.2 kg)
h is height (0.9 m)
g is acceleration due to gravity (9.81 m/s)

This gets fully converted to mechanical (or kinetic) energy, if there is no air resistance.

$$KE = PE = 1.2\text{ kg} \times 9.81\text{ ms}^{-1} \times 0.9\text{ m}$$

The answer will be in Joules because

$$ 1\text{ J} = 1\text{ kg}~\text{m}^2~\text{s}^{-1}$$