Question

How fast should a girl of 40 kg run so that her kinetic energy is 320J?

• A. 64 m/s
• B. 8 m/s
• C. 16 m/s
• D. 4 m/s

Answer 1

Answer: (D)

4 m/s

Given, mass $m=40kg,K.E=320J,v=?$
$K.E=\frac{1}{2}m{v}^2$

$320=\frac{1}{2}\times 40v^2$

$v^2=\frac{640}{40}=16$

$v=4m/s$
So, the girl of $40$ $kg$ should run at $4m/s$ so that her kinetic energy is $320J.$