A 950 kg automobile is at rest at a traffic signal. At the instant the light turns green, the automobile starts to move with a constant acceleration of 2.6 m/s2. At the same instant a 1950 kg truck, traveling at a constant speed of 6.8 m/s, overtakes and passes the automobile.
a. How far is the center of mass of the automobile-truck system from the traffic light at t = 3.0 s?
b. What is the speed of the com then?

(a)

(b)

Explanation:

Given data

950 kg automobile starts from rest with constant acceleration  2.6m/s²

1950 kg truck, traveling at a constant speed of 6.8 m/s

Automobile position

Velocity

Truck Position

Velocity of truck remain constant vt=6.8m/s

For Part (a)

The center of mass for Automobile Truck system:

For Part (b)

The velocity of center of mass for Automobile Truck system:

acceleration = (change in speed) / (time for the change)

change in speed = (20-120)= -100 m/s.

1.5 min = 90 sec

acceleration = -100/90 = -1.11 m/s^2.

we don't care about the 150kg or the 2,500 meters. they don't make any difference.

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hi there!

out of the two, (b) precision would be more reasonable.   however, both a and b could be pretty reasonable.

-awesomerepublic   : )