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PHY 231 HW6 F=ma View Basic/AnswersHW6 F=ma Begin Date: 2/18/2015 12:00:00 PM Due Date: 2/27/2015 11:59:00 PM End Date: 2/27/2015 11:59:00 PM
Problem 1:
Problem 7: Full solution not currently available at this time.
Cranes use a system of two pulleys to providemechanical advantage, which reduces the force theyneed to apply to lift a particular weight (two suchpossible configurations are shown in the figure). Acrane is attempting to lift a compact car with a massof m = 701 kg under the force of gravity.
Randomized Variables
m = 701 kg
VariableName Min Max Step Sample
Valuem 700 1250 1 701
Part (a) The crane's pulley system produces a mechanical advantage of 10. How many times, x, does the cable passover the pulley within the crane? (Assume that the tension in each segment of the rope is the same.)
Correct Algorithm: x = 5
Choice Info:
x = 5x = 5x = 5Buffer + or 0.15
Hints:3 hints available
There are two rope segments for each pass.Pulleys only change the direction of the tension.Draw a picture and then a Free Body Diagramof the lower pulley.
Part (b) Assuming that the positive ydirection is up, input an expression for the sum of the forces acting on the car inthe ydirection, in terms of the force produced by the crane's motor, Fc, and the given variables. Assume the motorpulls at a constant velocity.
Correct Equation: ΣFy = 10 Fc m g
Choice Info:
Valid Choices:10, Fc, g, m,
Partial Credit Choices with Feedback:
InValid Choices:t, α, θ, d, β, h, P, i, j, k, a, S,
Hints:3 hints available
Start with a free body diagram.There is 10 times mechanical advantage.There are two forces in the ydirection.
Part (c) What is the minimum force, in Newtons, the crane's motor must provide to begin to move the car?
Correct Algorithm: Fmin = m*9.81/10
Choice Info:
Fmin = 701*9.81/10
Fmin = 701*9.81/10
Fmin = 687.681Buffer + or 20.63043
Hints:2 hints available
It must overcome the weight at ten timesmechanical advantage.At minimum net force, a → 0.
Part (d) Assuming the crane's motor is producing a force of Fc = 1500 N on the car, what is the car's acceleration, inm/s2?
Correct Algorithm: a = (10*1500m*9.81)/m
Choice Info:
a = (10*1500701*9.81)/701a = (10*1500701*9.81)/701a = 11.588Buffer + or 0.34764
Hints:3 hints available
Net force equals mass times acceleration.You know the net force and mass.Write the second Newton’s law for the car.