Though it is not always the case, the force often opposes the motion of an object. it is exerted by a surface as an object moves across it or makes an effort to move across it.

a. gravitational
b. applied
c. fricttonal
d. normal

Though it is not always the case, the _frictional_ force often opposes the motion of an object. It is exerted by a surface as an object moves across it or makes an effort to move across it.

C. Frictional.

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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