2) In phase 1, a caraccelerates at a constant rate from rest, v0 = 0.0 m/s, atth
ID: 1759950 • Letter: 2
Question
2) In phase 1, a caraccelerates at a constant rate from rest, v0 = 0.0 m/s, atthe start line, x0= 0.0 m, to
its top speed,v1 = 180 km/h, during which it moves a distancex1 = 500 m. In phase 2, it moves at
the same top speedto the finish line at a distance x2 = 3.0 km fromthe start line.
a) Find the constantacceleration in phase 1, a1.
b) Find the time tocomplete phase 1, t1.
c) Find the timefrom the start to complete phase 2, t2.
d) Find the averagevelocity in phase 1, v1.
e) Find the averagevelocity in phase 1, v2.
f) Find the overallaverage velocity, v12.
g) Draw graphs of a(t), v(t) andx(t).
Explanation / Answer
Phase 1: Initial speed (vo) of the car in the phase1 = 0 Final speed (v) of the car in the phase1 = 180km/h = (180)(5/18)m/s = 50 m/s Distance (x1) traveled in the phase1 = 500m Phase 2:Acceleration (a1) of the car in thephase2 = 0, because it is moving with constant top speed. Distance (x2) traveled by the car in the phase2 =3.0km = 3000m (a) Constant acceleration (a1) of the car in the phase1is a1 = (v2 - vo2) /(2x1) = 2.5 m/s2 (b) Time taken to complete phase1 is t1 = v / a = (50m/s) / (2.5m/s2) = 20s (c) Time taken to complete phase2 is t2 = x2 /v = (3000m) / (50m/s) = 60s Total time taken = 20s + 60s = 80s (d) Average velocity in the phase 1 = (50m/s + 0)/2 = 25m/s (e) Average velocity in the phase2 is v2 = 50m/s
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