A 35 N block rests on a horizontal surface. The coefficients of static and kinetic friction between the surface and the block are 0.6 and 0.3, respectively. A horizontal string is attached to the block and a constant tension is maintained in the string. What is the force of friction acting on the block if the tension is 16 N? Answer in units of N. What is the force of friction acting on the block if the tension is 38 N? Answer in units of N.

(a) Frictional Force = 16 N

(b) Frictional Force = 10.5 N

Explanation:

(a) FOR TENSION OF 16 N:

First we find the static friction force (Fst):

Fst = (μs)(W)

Fst = (0.6)(35 N)

Fst = 21 N

Since, Tension < Fst

Frictional Force = Tension

Frictional Force = 16 N

(b) FOR TENSION OF 38 N:

Since, Tension > Fst

Frictional Force = Kinetic Friction = (μk)(W) = (0.3)(35 N) =  

Frictional Force = 10.5 N

d. platinum would have the greatest temperature increase because it has the lowest specific heat.

option number c is the right answer.