The stunt person for the new Mad Max movie launches a silver ball from an air cannon forward from vehicle travelling at 14.0 m/s. The launch speed of the air cannon is 25m/s. What is the speed of the ball right after it is launched relative to the ground?

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Answer 1 · 2017-09-27T09:06:41

See explanation.

The value of speed depends on the direction in which the vehicle is moving.

if the vehicle moves in the same direction in which the ball is fired then to calculate the relative speed you need to add the speeds:

#vec(v)=vec(v_(car))+vec(v_(canon))#

#v=14+25=39 m/s#

if the directions of the vehicle and cannon movement are opposite then you need to subtract the speeds:

#v=14-25=-11 m/s#

The negative sign of the velocity in the second point means that the ball moves in the direction opposite to the vehicle.