Question
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A car of mass 3.0 times 103 kg traveling at a speed of 20 m/s is passing a truck of mass 7.0 times 103 kg traveling at a speed of 10 m/s in the same direction along the same straight line. Calculate the speed of the center of mass of this system. A stream of water from a fire-fighter's hose hits a vertical wall. The firefighter knows that 16.9 kg of water are emitted from the hose per second, and that the water has a speed of 45.5 m/s when it hits the wall. At the instant when it hits the wall, the direction of the velocity vector of the water is 25.0 degrees BELOW the horizontal. Calculate the average force exerted by the water on the wall, assuming that the vertical component of the velocity vector of the water is unchanged but the horizontal component of the velocity vector is reversed when the water rebounds from the wall.
Explanation / Answer
Vcm=(m1v1+m2v2)/(m1+m2)
=13m/s in the same direction as the vehicles moving.
