Question

A 1,500 kg car’s speed changes from 30 m/s to 15 m/s after the brakes are applied. Calculate the work done onto the car from the brakes.

Answer 1

The work done onto the car is 506,250 J

The work done on a system implies an increase in the internal energy of the system as a result of some forces acting on the system from the outside.

From the parameters given:

• The mass of the car = 1500 kg
• The initial speed = 30 m/s
• The final speed = 15 m/s

The work done onto the car refers to the change in the kinetic energy (i.e. ΔK.E)

$\mathbf{=\dfrac{1}{2} mv_1^2 -\dfrac{1}{2} mv_2^2}$

$\mathbf{=\dfrac{1}{2} m(v_1^2 - v_2^2)}$

$\mathbf{=\dfrac{1}{2} \times 1500 \times (30^2 - 15^2)}$

= 506,250 J

Therefore, we can conclude that the work done on the car is 506,250 J

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