Question

The speed of a ball changes from $8m{s}^{-1}$ to $6m{s}^{-1}$ in 0.5 s on hitting a surface and bouncing back. Find the rate of change of speed of the ball?

• A. + 6 ${\text{ms}}^{-2}$
• B. - 6 ${\text{ms}}^{-2}$
• C. + 4 ${\text{ms}}^{-2}$
• D. - 4 ${\text{ms}}^{-2}$

Answer 1

The correct option is D - 4 ${\text{ms}}^{-2}$

Initial velocity = $8m{s}^{-1}$
Final velocity = $6m{s}^{-1}$
Time taken to change the velocity = 0.5 s

Rate of change of speed = $\frac{\text{Change in speed}}{\text{Total time}}$
Rate of change of speed = $\frac{\text{Final speed - Initial speed}}{\text{Total time}}$
= $\frac{6-8}{0.5}$ = - 4 ${\text{ms}}^{-2}$

(Negative sign indicates, body is decelerating)