Question

A 10kg boulder rests at the edge of a 100m cliff find kinitic energy.The rock rolls off the cliff and falls to the bottom. How much kinetic energy does the
rock possess at the bottom of the cliff.

Answer 1

A 10kg boulder rests at the edge of a 100m cliff.

Since the rock is at rest , its velocity is zero.

So, initial KE = ½ mu² = ½ m × 0² = 0 Joules.

Now, the rock rolls off the cliff and falls to the bottom.

• As per conservation of mechanical energy principle , the whole PE will be converted to KE at the bottom of cliff.

$KE = PE$

$\implies KE = m \times g \times h$

$\implies KE = 10 \times 10 \times 100$

$\implies KE = 10000 \: joule$

$\implies KE = 10 \: kilojoule$

So, KE at bottom of cliff is 100 kJ.