Question

A car moving at a speed of 30 kilometres per hour’s is brought to a halt in 8 metres by applying brakes. If the same car is moving at 60 km. per hour, it can be brought to a halt with same braking power in

• A. 8 metres
• B. 16 metres
• C. 24 metres
• D. 32 metres

Answer 1

Answer: (D)

32 metres

Answer 2

From $v^{2} = u^{2} - 2as$

$0 = u^{2} - 2as$

$s = \frac{u^{2}}{2a}$ ⇒ $s \propto u^{2}$ (if a = constant)

$\frac{s_{2}}{s_{1}} = \left( \frac{u_{2}}{u_{1}} \right)^{2} = \left( \frac{60}{30} \right)^{2} = 4$

⇒ $s _ { 2 } = 4 s _ { 1 } = 4 \times 8$ $S_{2} = 32$ metres.