# physic

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1) if you live 10.0 km from your school and the bus takes 0.53 h to reach the school driving due east, what is the average velocity of the bus?

2) To qualify for the finals in a racing event, a race car must achieve an average speed of 250 km/h on a track with a total length of 1600m. if a particular car covers the first half of the track at an average speed of 230 km/h, what minimum average speed must it have in the second half of the event to qualify?

• physic -

1. Velocity = Displacement / time
Displacement = Final position - initial position
Note that displacement does not have to equal distance if the bus travels in a zig-zag route.

2. Speed = distance / time
Total distance = 1600 m.
230 km/h = 230000 m/3600 s = 63.889 m/s
250 km/h = 250000 m/3600 s = 69.444 m/s
Time spent on first half of track
=800/63.889 s.
Total time permitted = 1600/69.444 s
Time left, t = 1600/69.444 - 800/63.889 s
So speed required = 800 m / t
Convert to km/h.

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