A racing car accelerates uniformly through three gear changes with the following average speeds:20ms-1 for 2.0s, 40ms -1 for 2.0s, and 60ms -1 for 6.0s.What is the overall average speed of the car?
Correct answer: C. 48 ms-1
- A. 12 ms-1
- B. 13.3 ms-1
- C. 48 ms-1
- D. 40 ms-1
Explanation
V - overall average speedS - a total distancet - a total timeV = S/tS = V1*t1 + V2*t2 + V3*t3V1, V2, V3 - average speeds for each gear changest = t1 + t2 + t3t1, t2, t3 - times for each gear changesFinally:V = (V1*t1 + V2*t2 + V3*t3)/( t1 + t2 + t3) = (20*2+40*2+60*6)/(2+2+6)=48 m/sAnswer: the overall average speed equals 48 m/s.
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