Apacking crate slides down an inclined ramp at constant velocity. thus we can deduce thata) a frictional force is acting on itb) a net downward force is acting on itc) a net upward force is acting on itd) it is not acted on by appreciable normal forcee) it is not acted on by appreciable gravitational force

A) a frictional force is acting on it

Explanation:

The crate is sliding down the inclined ramp at constant velocity: constant velocity means zero acceleration, a = 0. According to Newton's second law:

F = ma

this also means that the net force acting along the direction of the slope is zero.

Without frictional force, there would be only one force acting along this direction: the component of the weight of the crane parallel to the slope, acting downward:

where is the angle of the incline. Therefore, the net force along this direction would not be zero. In order to have a net force of zero, there must be another force acting upward on the crate: and the only force that is possibly acting on the crate against its direction of motion is the frictional force, whose magnitude must be equal to , in order to produce a net force of zero (and therefore, a zero acceleration).

in physics zero. in muscle fatigue could be high