Question

A 1500kg car has a kinetic energy of 4.2 x 10^5 J when it slows down to a speed where it has a kinetic energy of 2.3 x 10^5 J. How much work did the brakes do to slow the car down?

a) 1.9 x 10^5 J
b) 2.3 x 10^5 J
c) 1.3 x 10^5 J
d) 2.0 x 10^5 J

Answer 1

The work done by the brakes to slow down the car is the difference between the initial and final kinetic energies, calculated as 1.9 x 10^5 J.

Step-by-step explanation:

To calculate the amount of work done by the brakes to slow down the car, we can use the work-energy principle which states that the work done on an object is equal to the change in its kinetic energy. The initial kinetic energy (KEi) of the car is 4.2 x 105 J, and the final kinetic energy (KEf) after slowing down is 2.3 x 105 J.

The work done (W) by the brakes is the difference between the initial and final kinetic energy:

W = KEi - KEf

W = (4.2 x 105 J) - (2.3 x 105 J)

W = 1.9 x 105 J

Therefore, the brakes did 1.9 x 105 J of work to slow the car down, which corresponds to option (a).