Question

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

Answer 1

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

PE at the start= 200 x 9.8 x M  

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

kinetic energy= K.E = 0.5 x m x v²
m= mass
v= velocity

so, 1176M=0.5 x M x v² 
v= 48.49 m/s

Answer 2

Answer:

PE = mgh

= 200×9.8×M

= 1960M

% = 100-40= 60%

60% of 1960M = 1176M

__________________

KE = ½mv²

1176M = 1/2 M v²

=> v ≈ 49m/s

Hope it helps!