Question

A twig from a tree drops from a 200m high cliff on to a beach below.during its fall 40% twig's energy is converted into thermal energy.what is the speed with which the twig hits the beach?

Answer 1

Calculating for potential energy P.E=mgh
m=mass
g=acceleration due to gravity
h=height
Let the twig's mass be M 

therefore at the start, the twig has 200*9.8*M potential energy. 

During its fall 40% twig's energy is converted into thermal energy and the remaining 60% of this will turn into kinetic energy during the fall, giving us 1176M
Now the equation for kinetic energy, K.E is 0.5*m*v^2
m is mass
v is velocity

Therefore 1176M=0.5*M*v^2 (mass will divide out)
velocity is 48.49 m/s