# applied mechanics

posted by toly

a motorist driving his car at a speed of 72km/hr observes that the traffic lights ahead of him turns red if he comes to a halt at the traffic light 5seconds starting from first find the distance of the car from the light when the motorist observed the red light

1. Henry

Vo = 72000m/3600s = 20 m/s.

V = Vo + a*t = 0.
20 + a*5 = 0, a = -4 m/s^2.

V^2 = Vo + 2a*d.
V = 0, Vo = 20 m/s, a = -4 m/s^2,
d = ?.

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