Question

A car is moving with a uniform velocity of 54 kilometres per hour (km/h). What is the kinetic energy of a boy of mass 40 kg sitting in the car?

Answer 1

Step 1: Given data

Velocity of the car, $v=54km/h=\left(54\times \frac{5}{18}\right)m/s=15m/s$

Mass of the boy is, $40kg$

Step 2: Calculating kinetic energy

Kinetic energy is given as,

$KE=\frac{1}{2}m{v}^2$

where, $m$ is mass and $v$ is velocity

The velocity of the boy will be the same as the velocity of the car. Therefore, the kinetic energy of the boy can be calculated as,

$$\begin{gathered} KE=\frac{1}{2}\times 40kg\times {\left(15m/s\right)}^2 \\ KE=4500J \end{gathered}$$

Therefore, the kinetic energy of the boy is $4500J$.