Question

An object travels at $50m{s}^{-1}$ for the first 2 seconds and travels at $70m{s}^{-1}$ for the next 2 seconds. What is its average speed for the first 4 seconds?

• A. $50m{s}^{-1}$
• B. $70m{s}^{-1}$
• C. $60m{s}^{-1}$
• D. $56m{s}^{-1}$

Answer 1

The correct option is C $60m{s}^{-1}$

Given:
Speed in first 2 seconds = $50m{s}^{-1}$
Speed in the next 2 seconds = $70m{s}^{-1}$
Distance travelled in the first 2 seconds
= $50\times 2=100m$
Distance travelled in the next 2 seconds
= $70\times 2=140m$

$\Rightarrow$Total distance travelled$=100+140=240m$
Total time taken $=4s$
$\therefore \text{Average speed}=\frac{\text{Total distance covered}}{\text{Total time taken}}$$=\frac{240}{4}=60m{s}^{-1}$