Why is it harder to get something moving than to keep it moving?
1 answer:
You might be interested in
The momentum of a moving object is given by:
where m is the mass of the object and v its speed.
In this problem, the ball has a mass of
and its momentum is 
, so we can rearrange the previous equation to find the speed of the ball:
where m is the mass of the object and v its speed.
In this problem, the ball has a mass of
Answer:
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).