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O lvl Phy: Kinematics

A car starts from rest and accelerates constantly along a straight track at 4 m/s² for 2 s. It then travels with a constant speed for the next 3 s before it is brought to rest in 1 s by an increasing braking force.

(a) Using the speed-time axes shown below, sketch a grap to show how the speed of the car varies with time for its entire journey.



(b) Calculate the kinetic energy gained by the car in the first 1 s, given that the forward driving force provided by the engine is 3000 N.

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Answer:

(a)


(b) Using F=ma, and assuming no frictional force,
3000 = m(4)
mass of car = m = 750 kg

speed of car after 1s = 0 + 4(1) = 4 m/s

K.E. of car after 1s = ½ m v²
= ½ (750) (4)²
= 6000 J



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