Chapter 8, Problem 60A

Brakes are applied in bringing a 1200-kg car moving at 25 m/s to rest in 20.0 s. Show that the amount of braking force is 1500 N.

To determine

To Prove: the amount of braking force is 1500N.

Explanation of Solution

Given info:

The mass of the car is 1200kg.

Initial velocity of car, $u=25\text{m/s}$

Final velocity of car, $v=0$

Time, $t=20\text{ s}$

Formula used:

According to the newton’s second law of motion, the force is

  $F=ma$

Where, m is the mass and a is the acceleration of the object.

From first equation of motion:

  $a=\frac{v-u}{t}$

Calculation:

By substituting the values in the formula, the acceleration is,

  $\begin{array}{l}a=\frac{v-u}{t}\\ a=\frac{0-25}{20.0}\\ =-1.25{\text{m/s}}^2\end{array}$

  $\begin{array}{l}F=ma\\ =1200\text{kg}\times 1.25{\text{m/s}}^2\\ =1500\text{N}\end{array}$

Conclusion:

Hence, the braking force is 1500N.