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mechanics doubt AS

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halosh92:
thx so much guys!!!  ;)
and yep im a girl ;D

Phosu:
A car starts from rest at a point S on a straight racetrack. The car moves with constant acceleration for 20 s, reaching a speed of 25 m s–1. The car then travels at a constant speed of 25 m s–1 for 120 s. Finally it moves with constant deceleration, coming to rest at a point F.
(a) In the space below, sketch a speed-time graph to illustrate the motion of the car.(2)
The distance between S and F is 4 km.
(b) Calculate the total time the car takes to travel from S to F.(3)

A motorcycle starts at S, 10 s after the car has left S. The motorcycle moves with constant acceleration from rest and passes the car at a point P which is 1.5 km from S. When the motorcycle passes the car, the motorcycle is still accelerating and the car is moving at a constant speed. Calculate
(c) the time the motorcycle takes to travel from S to P,(5)
(d) the speed of the motorcycle at P.

could someone please explain how to solve c) part, i do have the ans, but i dont kno how they reached to it.

Kukkr:
lets just find out how much time did the car take to get to point P which is 1.5 km away from S

0.5 x 20 x 25 = 250m (this is how much the car traveled when it was accelerating, t = 20)
remaining is 1.5-0.25=1.25km or 1250m
25 x t = 1250 (we know from the question that the car was still moving at constant speed while the motor cycle passes it)
t = 50s

so 20 + 50 = 70s is the time the car took to reach point P...
but since the motorcycle left 10 seconds later... 70-10=60s

is 60 the correct answer?
I think there might be a better way to answer this question, but this is what I have come up with right now...

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