Question

A bus decreases its speed from $80km/hr$ to $60km/hr$ on a straight road in $5sec$. Find the magnitude of acceleration of the bus.

• A. 2.22m/s²
• B. 2.11 m/s²
• C. 1.11 m/s²
• D. 0 m/s²

Answer 1

The correct option is C

1.11 m/s²

Initial speed:
$u=80km/hr=80\times \frac{1000m}{3600s}$
$u=\frac{200}{9}m/s$

Final speed:
$v=60km/hr=60\times \frac{1000m}{3600s}$
$v=\frac{50}{3}m/s$

Time taken: $t=5s$

By definition of acceleration:
$a=\frac{v-u}{t}$
$a=\frac{600-800}{36\times 5}$
$a=-1.11m/s^2$

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