A 2000kg Cadillac had just started forward from a stop sign when it was struck f

Question

A 2000kg Cadillac had just started forward from a stop sign when it was struck from behind by a 1000kg Volkswagen. The bumpers became entangled and two cars skidded forward together until they come to rest. Officer Tom, responding to the accident, measured the skid marks to be 3.0 m long. He also took testimony from the driver that the Cadillac's speed just before the impact was 5.0 m/s. Officer Tom charged the Volkswagen driver with reckless driving. Should the Volkswagen driver be charged with exceeding the 14.0 m/s (50.0km/hr) speed limit? (uk =0.80

a) Draw a pictorial diagram of the situation (before and after collision) with all the variables (mass, velocities etc.) neatly labeled.

b) Draw a free-body diagram of the system (Cadillac +Volkswagen) after the collision. Clearly label all the forces

c) What is the velocity of the system (Cadillac +Volkswagen) immediately after the collision?

d) Finally, what is your conclusion? Was the Volkswagen driver speeding before the collision? Show your work to prove your conclusion.

Explanation / Answer

by conservation of momentum

initial momentum = final momentuum

force = ma

0.8 * mass * g = ma

0.8 * g = a

acceleration = 7.84 m/s

v^2 = u^2 + 2as

0 = u^2 - 2 * 7.84 * 3

velocity of (cadillac + volkswagen) immidiately after collision u = 6.858 m/s

2000 * 5 + 1000 * x = (2000 + 1000) * 6.858

speed of volkswagen x = 10.574 m/s

volkswagen driver was not speeding before collision

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