Question

A bus decreases its speed from $80kmh{r}^{-1}$ to $60kmh{r}^{-1}$ in 5 seconds. What is the acceleration of the bus?

• A. 2.22 $\frac{m}{s^2}$
• B. 2.11 $\frac{m}{s^2}$
• C. 1.11 $\frac{m}{s^2}$
• D. 0 $\frac{m}{s^2}$

Answer 1

The correct option is C

1.11 $\frac{m}{s^2}$

Initial speed $u=80\frac{km}{hr}=80\times \frac{1000}{60\times 60}=\frac{800m}{36s}$

Final speed $v=60\frac{km}{hr}=60\times \frac{1000}{60\times 60}=\frac{600m}{36s}$

Time taken $t=5s$

$a=\frac{v-u}{t}$ $=\frac{600-800}{36\times 5}$$=-1.11\frac{m}{s^2}$

Here sign of acceleration is negative which shows that the speed is decreasing and acceleration is in the opposite direction of the motion.