PhysicsBowl 2016 Q5

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PhysicsBowl 2016

5) Question 5 asks us to find the tension in the string in this problem. Note that the pulley's mass is not given, so we will assume it to be negligible. Since the blocks do not move, they are in static equilibrium

Let's start out with a force drawing of the block of mass m = 6 kg.

Where T is tension force, m is mass, g is acceleration due to gravity, and F[net] is the net force

Intuitively, this seems correct. Since the net force is 0, we think that the Tension should be equal in magnitude and opposite in direction with the object's weight.

To be thorough, let's also look at the block of mass M = 14 kg. We can draw the force diagram and solve all its forces.

Where T is tension force, m is smaller mass, g is acceleration due to gravity, N is normal force, M is larger mass, and F[net] is the net force

Remember that although the large mass is on the ground, the tensional force still acts on it. Since there is a tension force, the normal force is reduced.

All values work and seem reasonable, so our initial intuition was correct.

Answer: B