Question

If a body moves for 2 s with 15 m/s velocity towards east and then moves with 5 m/s velocity for 8 s towards north, then average velocity is :

• A. 5 m/s
• B. 15 m/s
• C. 30 m/s
• D. 7.5 m/s

Answer 1

Answer: (A)

5 m/s

Answer 2

Key Idea: $\text{Average}\,\text{velocity}\,\text{=}\,\frac{\text{Displacement}}{\text{Time}\,\text{taken}}$
Let body move along AB, then BC.
Distance travelled in 2s.
${{\text{S}}_{1}}=15\times 2=30\,m$
Distance travelled in 8s
${{S}_{2}}=5\times 8=40\,m$
$\therefore$ Displacement $AC=\sqrt{{{(30)}^{2}}+{{(40)}^{2}}}$
$=\sqrt{900+1600}=\sqrt{2500}$
$=50\,m$
Hence average velocity
$=\frac{\text{displacement}}{\text{time}\,\text{taken}}$
$=\frac{50}{8+2}=\,5\,m/s$