Question

A $50kg$ trolley initially moving at a speed of $15m/s$ along a rail track takes $20m$ to stop with the brakes on.
What is the approximate coefficient of kinetic friction between the tracks and the wheels of the trolley?

• A. $\mu =0.04$
• B. $\mu =0.57$
• C. $\mu =1.14$
• D. The situation is impossible
• E. None of the above

Answer 1

Answer: (B)

$\mu =0.57$

Given : $m=50$ kg $S=20$ m $u=15$ m/s $v=0$ m/s

Using $v^2-u^2=2aS$

$\therefore$ $0-(15{)}^2=2a\times 20$ $⟹a=-5.63$ $m/s^2$

Magnitude of kinetic friction $f=\mu mg$

$\therefore$ $m|a|=f=\mu mg$

$⟹$ $\mu =\frac{|a|}{g}=\frac{5.63}{9.8}=0.57$