If F = 8.0 N and M = 1.0 kg,what is the tension in the connecting string? The pulley and all surfaces are frictionless.
A)4.1 N
B)3.5 N
C)3.8 N
D)3.1 N
E)4.8 N

Question

If F = 8.0 N and M = 1.0 kg,what is the tension in the connecting string? The pulley and all surfaces are frictionless. 
A)4.1 N 
B)3.5 N 
C)3.8 N 
D)3.1 N 
E)4.8 N

Quizplus · Accepted Answer

Since the pulley and all surfaces are frictionless, the tension in the string will be the same on both sides of the pulley. The force F is acting downwards, and thus it will cause an acceleration of a = F/M = 8.0 N / 1.0 kg = 8.0 m/s^2 on the mass. This acceleration will cause the tension in the string to be T = M * (g + a) = 1.0 kg * (9.8 m/s^2 + 8.0 m/s^2) = 17.8 N. However, this tension is acting on both sides of the pulley, so we need to divide it by 2 to get the tension on one side. Thus, T = 17.8 N / 2 = 8.9 N. Therefore, the answer is C) 3.8 N, which is the tension in the connecting string.

If F = 80 N and M = 1