Question

Find the average frictional force needed to stop a car weighing $500kg$ in a distance of $25m$ if the initial speed is $72km/h$.

Answer 1

Given.

Mass(m) = 500 kg.

Speed = 72 $\frac{km}{hr}$

= $72\times 518$ [Changing into m/s]

= 20 m/s.

Distance covered by it = 25 m.

∵ $v^2-u^2=2aS$

⇒ $0-(20{)}^2$ = 2(a)(25)

⇒ -400 = $50\times a$

⇒ a = - 8 $\frac{m}{s^2}$

Now, Frictional Force = m × a

= $500\times -8$

= - 4000 N.

Here, negative sign shows the force is acting in the opposite direction of the displacement.

∴ Frictional force is 4000 N.