Problem 5.30 Frictonal forces An 80N box initially at rest is pulled by a horizontal ropeon a horizontal table. The coefficients of kinetic and staticfriction between the box and the table are 1/4 and 1/2.respectively. What is the friction force on this box if theis a) 0 N b)25 N c) 39 N d) 41 N e) 150 N. Problem 5.30 Frictonal forces An 80N box initially at rest is pulled by a horizontal ropeon a horizontal table. The coefficients of kinetic and staticfriction between the box and the table are 1/4 and 1/2.respectively. What is the friction force on this box if theis a) 0 N b)25 N c) 39 N d) 41 N e) 150 N.
Explanation / Answer
weight of the box W = 80N normal reaction n = 80N coefficient of kinetic friction k = 1/4 coefficient of static friction frictions = 1/2 static friction fs =sn = (1/2)*80N = 40N kinetic friction fs =sn =(1/4)*(80N) = 20N = (1/2)*80N = 40N If applied force F < fs , then friction isfs If applied force F > fs , then friction isfk from these conditions calculate the friction force forall the five cases. from these conditions calculate the friction force forall the five cases.