Question

A motor car runs with a speed of $7m{s}^{-1}$ is stopped by applying brakes. Before stopping, the motor car moves through a distance of 10m. show the total resistance of the motion of the car when breaks are on the one-fourth of the weight of the car

• A. $\frac{2}{6}$ of its weight
• B. $\frac{2}{4}$ of its weight
• C. $\frac{1}{5}$ of its weight
• D. $\frac{1}{4}$ of its weight

Answer 1

The correct option is D $\frac{1}{4}$ of its weight

For a motor car:

$u=7$m/s; $v=0$; $s=10$m

Using $v^2=u^2+2$as, we get

$a=\frac{v^2-u^2}{2s}=\frac{0-7^2}{2\times 10}$

$=-2.45m/s^2$

$a=-g/4$

$-f=-ma=mg/4$

$1/4^{th}$ of the weight of the car.