Question

A teenager pulls 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 teenager pulls the wagon?

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

Answer 1

Answer: (C)

45.0 Joules

Let the mass of wagon be $m$ and its velocity when young child was pulling be $v$.

Thus initial kinetic energy of the wagon $K_i=\frac{1}{2}m{v}^2=5$ J

Velocity of wagon when the teenager is pulling $V=3v$

New kinetic energy $K_f=\frac{1}{2}m(3v{)}^2=9K_i=9\times 5=45$ J