Question

A body of mass 2 kg has a potential energy of 800 J when it is at a certain height. If it begins to fall, its velocity when its Kinetic energy and Potential energy are equal is

• A. $4m{s}^{-1}$
• B. $400m{s}^{-1}$
• C. $20m{s}^{-1}$
• D. $80m{s}^{-1}$

Answer 1

The correct option is C $20m{s}^{-1}$

Total energy $=$ Potential Energy $+$ Kinetic Energy $=800J$

At certain height when Potential Energy $=$ Kinetic Energy $=400J$

Kinetic Energy $=\frac{1}{2}m{v}^2=400$

$\Rightarrow v=20m/s$