8) A packing crate slides down an inclined ramp at constant velocity. Thus we ca

Question

8) A packing crate slides down an inclined ramp at constant velocity. Thus we can deduce that A) it is not acted on by appreciable gravitational force. B) it is not acted on by appreciable normal force. C) a net downward force is acting on it. D) a frictional force is acting on it. E) a net upward force is acting on it.

The answer is D- a frictional force is acting on it. I am confused- I thought a constant velocity means that no net forces are acting on the object. So why is it true that a frictional force is acting on it? Wouldn't this make the velocity a non constant value?

Explanation / Answer

8)

answer D) frictional force is acting on it

Explanation :

There are three forces acting on the body :

1) gravitational force vertically down

2) normal force from the incline perpendicular to the incline

3) friction force up the incline

As the crate slides down with constant velocity, the net force on it is 0.

So, net force due to all the 3 forces is 0

NOTE : the frictional force up the incline is cancelled by the component of force of gravity down the incline

The normal force cancels out the other component of the force of gravity.

Thus the net effect is 0 force

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