Answer:C
Explanation:
When a constant horizontal force is applied to the box, box started moving in the horizontal direction such that it moves with constant velocity
Constant velocity implies that net force on the box is zero
i.e. there must be an opposing force which is equal to the applied force and friction force can serve that purpose.
So option c is the correct choice.
Answer: P= W/t so P=50/20 =2.5 W
Let's supose that your object is the orange rectangle rotating around the blue circle (see picture attached)
r = 1.0 [m] is the radius of the circle (it's R in your problem).
ω [rad/s] - is the angular velocity of the object, it is measured in radians per second. We will compute it from the data you have
v [m/s] - is the tangential/linear speed, it is measured in meters per second
We know that the rotational speed is 10 revolutions per 4 seconds.
10/4 rev/s = 2.5 rev/s
We convert rev/s in rad/s and we get:
2.5 rev/s = 15.708 rad/s
So we found our angular speed: ω = 15.708 rad/s
The relationship between v and ω is:
v = ω · r = 15.708 · 1 = 15.708 m/s
Answer: the magnitude of the velocity around the circle is 15.708 m/s
The answer, I believe, is, "B. When particles collide, no energy is lost."