KCET · Physics · Rotational Motion
A car moves from A to B with a speed of \( 30 \mathrm{kmph} \) and from B to A with a speed of \( 20 \mathrm{kmph} \).
What is the average speed of the car ?
- A \( 25 \mathrm{kmph} \)
- B \( 24 \mathrm{kmph} \)
- C \( 50 \mathrm{kmph} \)
- D \( 10 \mathrm{kmph} \)
Answer & Solution
Correct Answer
(B) \( 24 \mathrm{kmph} \)
Step-by-step Solution
Detailed explanation
Given, speed of car from \(\mathrm{A}\) to \(\mathrm{B}=30 \mathrm{kmph}^{-1}=v_{1}\)
Speed of car from \(\mathrm{B}\) to \(A=20 \mathrm{~km} h^{-1}=v_{2}\)
Average speed of car \(=\frac{2 v_{1}+v_{2}}{v_{1}+v_{2}}=\frac{2 \times 30 \times 20}{30+20}=\frac{1200}{50}=24\)
Average speed of car \(=24 \mathrm{kmph}\)
Speed of car from \(\mathrm{B}\) to \(A=20 \mathrm{~km} h^{-1}=v_{2}\)
Average speed of car \(=\frac{2 v_{1}+v_{2}}{v_{1}+v_{2}}=\frac{2 \times 30 \times 20}{30+20}=\frac{1200}{50}=24\)
Average speed of car \(=24 \mathrm{kmph}\)
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