Question

The following setup (Fig. 2) is being observed where a block of mass m is located at the point A, 1 m above the ground. It travels down a smooth track to the point B, and at no point in its journey does the block lose contact with the track. There is no air-resistance.

(a) State two non-conservative forces you’ve heard of. Indicate whether these non-conservative forces are acting on

the system. Hint: Read the problem statement carefully.

1.0 m B

(b) You are told that the work done by non-conservative forces acting on this system is zero. So you realize that the total mechanical energy of the system is conserved. Using energy conservation, calculate the velocity of the mass as it reaches the point B.

Beyond the point B (not shown in the diagram) the track continues as a horizontal path. This path turn out to be rough and has a friction coefficient μk = 0.2.

(c) Explain the meaning of the subscript k in μk.
(d) Explain why the total energy of the system is not conserved as the block moves on the horizontal track beyond

the point B. Restrict your response to within two lines.
(e) Use the work-energy theorem to compute the distance travelled by the block from the point B before coming to

rest. Hint: You will have to account for the work done by friction.