Question

A teenager pulls a wagon so that it moves $3$ times as fast as when a young child pulls it.
If the wagon has $5.0$ Joules of kinetic energy when the child pulls the wagon, how much kinetic energy does it have when the teenage pulls the wagon?

• A. $15.0Joules$
• B. $8.0Joules$
• C. $45.0Joules$
• D. $5.0Joules$
• E. $1.67Joules$

Answer 1

The correct option is C $45.0Joules$

Let velocity of wagon when young child pulls it , is $v$ ,therefore velocity of wagon given by the teenager will be $3v$ ,

kinetic energy when child pulls the wagon , $K=1/2m{v}^2$

or $5.0=1/2m{v}^2$ .......eq1

kinetic energy when teenager pulls the wagon ,$K^{\prime }=1/2m(3v{)}^2$

or $K^{\prime }=9/2m{v}^2$ .......eq2

dividing eq2 by eq1 ,

$K^{\prime }/5.0=9$

or $K^{\prime }=9\times 5.0=45.0J$