Dynamics A 1200-kg trailer is hitched to a 1400-kg car. The car and trailer are
ID: 1861212 • Letter: D
Question
Dynamics
A 1200-kg trailer is hitched to a 1400-kg car. The car and trailer are travelling at 72 km/h when the driver applies the brakes on both the car and the trailer. Knowing that the braking forces exerted on the car and the trailer are 5000 N and 4000 N respectively, determine (a) the distance traveled by the car and trailer before they come to a stop, (b) the horizontal component of the force exerted by the trailer hitch on the car. A trailer truck enters a 2 percent uphill grade traveling at 72 km/h and reaches a speed of 106 km/h in 300 m. The cab has a mass ofExplanation / Answer
a)
72 km/h = 72*1000/(60*60) m/s = 20 m/s
Total braking force = 5000+4000 N = 9000 N
Total mass = 1200+1400 kg = 2600 kg
F = ma
a = F/m = 9000 / 2600 = 3.46 m/s^2
v^2 = u^2 - 2as
0 = 20^2 - 2*3.46*s
s = 57.8 m
b)
Average braking force on trailer wheels = 9000*1200/2600 = 4153.8 N
Net force in hitch = 4153.8 - 4000 = 153.8 N = 0.154 kN
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