Coursera – “Engineering Systems in Motion: 2D Dynamics”
Spring 14 - Week One Quiz Solution – Modules 1-8
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Problem 1)
A local amusement park learned that you successfully completed Dr. Whiteman’s
Coursera course on 2D Dynamics. They decide to hire you to redesign one of their rides.
The ride consists of a passenger compartment on a rail. The passenger compartment is
traveling 60 ft/sec on a straight rail. A stopping mechanism then applies a constant
deceleration of 10 ft/sec2 for a period of 5 seconds. At that point, the passenger
compartment is given an immediate constant acceleration of 4 ft/sec2. How long will it
take for the passenger compartment to return to its original velocity of 60 ft/sec?
ANSWER: b) 12.5 seconds
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Problem 2)
Now for a different ride design, you are now concerned with the passenger compartment
coming to a safe stop. The passenger compartment is traveling with an initial velocity of
125 ft/sec. In an emergency, the brakes can be applied to lock all 4 wheels. When this
happens, Coulomb friction with a force proportional to the coefficient of friction, µ,
times the normal force, brings the compartment to a complete stop. Use the acceleration
due to gravity, g = 32.2 ft/sec2. If the compartment is required to come to a complete
stop in 8 seconds during an emergency, what is the required friction coefficient, µ?
ANSWER: c) µ = 0.485
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Problem 3) The blocks shown below slide together down the incline at the same
acceleration. The coefficient of friction, μ, between block D and the incline surface is
0.5. The coefficient of friction, μ, between block F and the incline surface is 0.1. Find
the acceleration of the blocks and the force between them. ANSWER: c)
28.0 N
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