Question

Find the braking force needed to bring a 4500 kg truck to a stop from a speed of 20 m/s in 9 s.

Answer 1

Given

Mass of the truck, m=4500 kg

Speed of th etruck, u=20 m/s

Time required , t=9 m/s

To find

The braking force

Explanation

Since the car stops so the final velocity is v=0

Thus the acceleration of the truck is

$\begin{gathered} a=\frac{v-u}{t} \\ \Rightarrow a=\frac{0-20}{9}=-2.22m/s^2 \end{gathered}$

The negative sign says that the speed is decreasing i.e. decelaration is occuring

Thus the braking force is (considering only the magnitude)

$\begin{gathered} F=ma \\ \Rightarrow F=4500\times2.22=9990\text{ N} \end{gathered}$

Conclusion

The braking force is 9990 N