A Truck of 600 kg is moving on a level road at 30 m/s.
i. How large a retarding force (assumed constant) is required to stop it in a distance of 70 m?
ii. What is the minimum coefficient of friction between tires and roadway if this is to be possible?
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Explanation:
speed:
v = 30 + a t
what is a when v = 0
-30 = a t
a = -30/t
distance:
70 = 30 t + (1/2) a t^2
70 = 30 t -(15/t) t^2
70 = 15 t
t = 14/3 seconds to stop
a = -30/t = -90/14 m/s^2 = -45/7
then F = m a
F = -600 (45/7) Newtons
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