Question

A spring is kept compressed by a toy car of mass $150g$. On releasing the car, it moves at a speed of $0.2m/s$. So, the elastic potential energy of the spring is

Answer 1

Step 1: Given data

Mass of the toy car (m) = $150g=0.15kg$

Speed of the car (v) = $0.2m/s$

Step 2: Calculate the elastic potential energy of the spring

When the car is released, the spring starts to uncompress itself and thus the potential energy stored in the spring will be converted into the kinetic energy of the toy car. By energy conservation, all of the potential energy will be converted completely into the kinetic energy of the car and thus,
The elastic potential energy of spring = Kinetic energy gained by the toy car

We know that the kinetic energy of the cart will be $=\frac{1}{2}m{v}^2$.

Thus, the elastic potential energy of the spring will also be $=\frac{1}{2}m{v}^2$.

On substituting the values, we get:

$$\begin{gathered} =\frac{1}{2}\times 0.15\times {\left(0.2\right)}^2 \\ =0.003J \end{gathered}$$

Thus, the elastic potential energy of the spring is $0.003J$ or $3mJ$.