Question

A bus increases its speed from 20 km/h to 50 km/h in 10 seconds. Its acceleration is:
(a) 30 m/s² (b) 3 m/s² (c) 18 m/s² (d) 0.83 m/s²
Choose the correct answer.

Answer 1

Initial speed of the bus = 20 km/h = $20\times \frac{1000\mathrm{m}}{60\times 60\mathrm{s}}=\frac{50}{9}\mathrm{m}/\mathrm{s}$

Final speed of the bus = 50 km/h = $50\times \frac{1000\mathrm{m}}{60\times 60\mathrm{s}}=\frac{125}{9}\mathrm{m}/\mathrm{s}$

Time taken by the bus to change its speed = 10 seconds

Acceleration of the bus = $\frac{\mathrm{Final}\mathrm{Speed}-\mathrm{Initial}\mathrm{Speed}}{\mathrm{Time}\mathrm{taken}}=\frac{{\displaystyle \frac{125}{9}-\frac{50}{9}}}{10}=\frac{5}{6}\mathrm{m}/{\mathrm{s}}^2=0.83\mathrm{m}/{\mathrm{s}}^2$

Hence, the correct answer is option D.