RI sec 3 1997 EOY P1 Q13
The diagram shows the speed-time graph of a motorist.
(i) Calculate the speed of the motorist after 6 seconds.
(ii) Calculate the time taken to cover a distance of 144 m.
(iii) Calculate the retardation of the motorist.
(iv) Sketch the acceleration-time graph of the motorist for the whole 35 seconds of the motion.
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Answer:
(i) Acceleration = 12/10 = 1.2 m/s2
Speed = u + at
= 0 + 1.2 * 6
= 7.2 m/s
(ii) For the first 10 s, distance travelled = ½ (12) (10) = 60 m
let the time taken = t
hence, 60 + (t - 10) * 12 = 144
(t - 10) * 12 = 84
t - 10 = 7
t = 17 s
(iii) Acceleration of the last 5 seconds = (12 - 0) / (30 - 35) = -12 / 5 m/s2
Hence, retardation = 2.4 m/s2
(iv)
