Physics · Forces and Motion
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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?
- A
12 ms–1
- B
13.3 ms–1
- C
48 ms–1
- D
40 ms–1
V - overall average speed
S - a total distance
t - a total time
V = S/t
S = V1*t1 + V2*t2 + V3*t3
V1, V2, V3 - average speeds for each gear changes
t = t1 + t2 + t3
t1, t2, t3 - times for each gear changes
Finally:
V = (V1*t1 + V2*t2 + V3*t3)/( t1 + t2 + t3) = (20*2+40*2+60*6)/(2+2+6)=48 m/s
Answer: the overall average speed equals 48 m/s.
This option is incorrect. It underestimates the average speed by using incorrect calculations.
This option is incorrect. It may result from summing the speeds directly without considering the time intervals.
This is the correct option. By correctly calculating the total distance traveled and dividing it by the total time, you obtain the overall average speed.
This option is incorrect. It results from an incorrect application of the average speed formula.
Tagged under Physics · Forces and Motion · 2014