Question

A nut of mass 0.2 kg falls from the ceiling of an elevator moving down with a uniform speed 5 m/s . It hits the floor and does not rebound. What is the heat produced by the impact if the height of the elevator is 4 m ?

• A. 0.8 J
• B. 10.5J
• C. 8 J
• D. 4 J

Answer 1

The correct option is C 8 J

Solving in the frame of lift.

Velocity of nut before striking to the floor is to be calculated for finding energy of the nut before collision.

So $V=\sqrt{2gh}$ velocity of free fall.

So $V=\sqrt{2\times 10\times 4}=\sqrt{80}$

Energy before collision is only kinetic energy and is fully converted to heat energy, due to law of conservation of energy.

$K.E.=\frac{1}{2}\times 0.2\times (\sqrt{80}{)}^2$

$K.E.=8J$

So heat produced will be $8J$.

So best possible answer is option C.