Question

A train accelerating uniformly from rest attains a maximum speed of $40 \,ms ^{-1}$ in $20\, s$. It travels at the speed for $20\, s$ and is brought to rest with uniform retardation in further $40\, s$. What is the average velocity during the period?

• A. 80 m/s
• B. 25 m/s
• C. 40 m/s
• D. 30 m/s

Answer 1

Answer: (B)

25 m/s

Answer 2

$S _{1}=\left(\frac{ u + v }{2}\right) t$ $=20 \times 20=400 \,m$ $S _{2}=40 \times 20=800\, m$ $S _{3}=\left(\frac{ u + v }{2}\right) t$ $=20 \times 40=800 \,m$ Total displacement $=2000 \,m$ Total time taken $=80\, m$ $V =\frac{2000}{80}=25 \,m / s$ Total time taken $=80\, m$ $V =\frac{2000}{80}=25\, m / s$