Question

A car travels at a constant velocity of 20.0 meters/second for 15 seconds. What is the power of the car if the initial force applied to it was 95 newtons?

Answer 1

The correct answer to the question is 1900 Joule.

CALCULATION:

As per the question, the velocity of the car v = 20.0 m/s.

The time taken by the car t = 15 seconds.

The initial force applied on the car F = 95 N.

We are asked to calculate the power of the car.

Let the displacement of the car is denoted as S.

Let the power of the car is P.

The power of a car is defined as the word done by the car per unit time.

Hence, the power P = $\frac{W}{t}$

                                 = $\frac{\vec F.\vec S}{t}$

                                 = $\vec F.\frac{S}{t}$

                                 = $\vec F.\vec v$

                                 = $Fvcos\theta$

Here, $\theta$ is the angle between force and velocity.

If $\theta= 0^{0}$, then P = Fv.

Hence, the power of the car is calculated as -

                                          P = 95 N × 20.0 m/s

                                             = 1900 Joule.

Answer 2

Work done by the force = Force x displacement. Power = work done/time = F.s/t = F.u.t/t = F.u = 95 x 20 = 1900J.                                                                                                                                                                                               {S=ut because acceleration is zero since car is moving at constant velocity}.