Question

A tv tower is 40m high.A mass of $5kg$ is dropped from its top . calculate the potential energy at the top and kinetic energy just before it hits the ground $($take $g=10m/s^2)$

• A. Each is $1000$ joule
• B. Each is $2000$ joule
• C. Each is $3000$ joule
• D. Each is $500$ joule

Answer 1

The correct option is B Each is $2000$ joule

At the top of the tower, just fter dropping, the $PE$ of the body will be maximum and $KE$ will be $0$, i.e.,;
Total Energy: $PE+KE$
$:mgh+0$
$:5\left(10\right)\left(40\right)$
$:2000J$
$2kJ$
Now, just before it hits the gournd, the KE of the body will be maximum and the PE will be zero.
Total Energy: $PE+KE=2000J:0+KE$ (According to Law of COnservation of Energy)
$\Rightarrow KE=2000J$