Question

A ball of 10kg falls from rest from a height of 150m, Neglating air resistance, calculate its kinetic energy after falling a distance of 40m. Take g=10m/s

Answer 1

Answer: $3920\ J$

Explanation:

Given

mass of ball m=10 kg

It is placed at a height of 150 m

It is dropped from the height and allowed to free fall for 40 m

Velocity acquired by the ball during this fall is given by $v^2-u^2=2as$

Insert u=0, a=g

$\Rightarrow v^2-0=2\times 9.8\times 40\\\Rightarrow v=\sqrt{784}\\\Rightarrow v=28\ m/s$

Kinetic energy at this instant

$K.E.=\dfrac{1}{2}\times 10\times 28^2\\\\\Rightarrow K.E.=3920\ J$