Question

A body is moving with a speed of 1 ms^-1 and a force F is needed to stop it in a distance x. If the speed of the body is 3 ms^-1, the force needed to stop it in the same distance x will be

• A. 1.5F
• B. 3F
• C. 6F
• D. 9F

Answer 1

Answer: (D)

9F

Answer 2

s = $\frac{u^{2}}{2a} = \frac{mu^{2}}{2F}$

i.e. Retarding force µ u²

$\frac{F_{2}}{F_{1}} = \left( \frac{u_{2}}{u_{1}} \right)^{2} = \left( \frac{3}{1} \right)^{2}$ ̃ F₂ = 9F₁