Question

A car is travelling with uniform speed on a flyover bridge which is a part of vertical circle whose radius of curvature is $60m$. A person in that car feels $75\%$ decrease in his weight when the car is crossing highest position. The speed of car at that position is:

• A. $28m/s$
• B. $21m/s$
• C. $14m/s$
• D. $7m/s$

Answer 1

The correct option is B $21m/s$

Since the weight decreased by $75$%, the centripetal force acting upwards must be equal to $\frac{3mg}{4}$

Hence $\frac{m{v}^2}{R}=\frac{3mg}{4}$
$⟹v=\sqrt{\frac{3gR}{4}}$

$⟹v=21m/s$