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course Phy 231
10/23/2011 @ 10:00p.m.
As discussed in class you should master Introductory Problem Set 5 before next Monday's class.You should also submit your answers to the following questions:
`q001. For each of the given objects on the various inclines estimate, based on a sketch as opposed to a formula, the parallel and perpendicular components of the object's weight as a percent of its weight. Use your estimated percents to find the component of each weight parallel to the incline, and perpendicular to the incline.
A car weighing 20 000 Newtons on an incline making angle 12 degrees with horizontal.
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For all of these, positive is down the ramp for the parallel component, and positive is “down” for the perpendicular components.
Par = 30%, 6,000N
Per = 95%, 19,000N
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A hotwheels car of weight 80 000 dynes on an incline whose angle with horizontal is 20 degrees.
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Par = 50%, 40,000dynes
Per = 90%, 72,000 dynes
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A block of weight 30 pounds on a 37 degree incline.
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Par = 60%, 18 lbs
Per = 70%, 21 lbs
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`q002. If the car in the first question experiences a frictional force which is 2% of the perpendicular component of its weight, then what is the magnitude of the frictional force?
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-380N
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If the car is coasting downhill what is the sum of the parallel component of its weight and the frictional force?
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18,620N
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@& You estimated the parallel foce to be about 6 000 N and the frictional force as -380 N.
You don't get 18 000 N out of that.*@
If the car is coasting uphill what is the sum of the parallel component of its weight and the frictional force?
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-19,380N
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@& I see what you're doing and except for being way off on the parallel component of the weight, you're thinking correctly.*@
`q003. If the hotwheels car in the first question is attached by a light thread to a washer weighing 20 000 dynes and suspended over a pulley at the lower end of the ramp, then if friction is ignored what is the net force acting in the direction down the ramp?
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60,000 dynes
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Answer the same question assuming that the washer is suspended from a pulley at the top of the ramp.
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20,000 dynes
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@& Again right idea but I'm worried about your parallel weight component.*@
`q004. How much frictional force would it take to hold he block in the first question stationary on the incline?
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-18lbs
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What is this force as a percent of the weight of the block?
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60% of its weight.
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"
@& Check my notes. You're doing most of the right things but I don't think you're getting that parallel component right.*@