A cord runs around two massless, frictionless pulleys. A canister with mass m =
ID: 1884038 • Letter: A
Question
A cord runs around two massless, frictionless pulleys. A canister with mass m = 32 kg hangs from one pulley, and you exert a force F on the free end of the cord. (a) What must be the magnitude ofF if you are to lift the canister at a constant speed? (b)To lift the canister by 1.2 cm, how far must you pull the free end of the cord? During that lift, what is the work done on the canister by (c) your force (via the cord) and (d) the gravitational force? (Hint: When a cord loops around a pulley as shown, it pulls on the pulley with a net force that is twice the tension in the cord.)
Explanation / Answer
mass = m = 32 kg
a) on pulley 1 , constant speed so net force is zero
2T - mg = 0
T = mg / 2 = 32 *9.8 /2 = 156.8 N
Hand - cord =0
T - F = 0
F = T = 156.8 N
B) displacement = s = 2*0.012 = 0.024 m
c) WF = F * S = 156.8 * 0.024 = 3.76 joules
d) Wg = - mg d = -3.76 j
T
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