Question

A car moving with a speed of 40 km/h can be stopped by applying brakes after at least 2 m. If the same car is moving with a speed of 80 km/h, what is the minimum stopping distance?

• A. 4 m
• B. 6 m
• C. 8 m
• D. 2 m

Answer 1

Answer: (C)

8 m

Answer 2

For the 1st case, u = 40 km/h = $40 \times \frac{5}{18} \text{ m/s}$

From motion'sthird equation, we get

v2 - u2 = 2as

v2 = u2 + 2as

$0 = \left(40 \times \frac{5}{18}\right)^2 + 2a(2)$

$a = -\frac{1}{4}\left(\frac{100}{9}\right)^2 - 1$

For the 2nd case -

u = 80 km/h

v2 - u2 = 2as

v2 = u2 + 2as

$0 = \left(80 \times \frac{5}{18}\right)^2 + 2as$

On solving the equation, we get s=8m.

Hence, option (C) is the correct answer.