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course phy201
`q001. A velocity of 5 m/s at 30 degrees is added to a velocity of 1 m/s at 120 degrees, What is the resulting velocity?
5/30 x/120
21m/s
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Per Introductory Problem Set 5 you need to find the components of both vectors, add them and use the totals to find the magnitude and direction of the resultant.
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`q002. Sketch, reasonably to scale, the force vectors acting on a system of two masses, one of mass 10 kg on a horizontal frictionless surface and the other of 2 kg suspended by a string over a pulley, with the other end of the string connected to the 10 kg mass. Between the 10 kg and the mass the string is horizontal. The tension in the string is considered internal to the system; the tension pulls one way on the 10 kg mass and the other way on the 2 kg mass, but you don't need to sketch the tension vector.
How many force vectors did you sketch?
2
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Identify each of these force vectors and explain what the source of each force is.
One is the force vector of the 2kg weight and the other is the force vector of the 10 kg vector with gravity being the acceleration
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The surface supports the 10 kg mass. This requires a force, which should be included in your sketch.
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List the vectors in order, from the smallest to the largest.
10kg weight vector
2kg weight vector
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10 kg and 20 kg aren't weights; the weights would be 98 N and 196 N.
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What is the magnitude of each of your vectors, as a percent of the largest?
F=ma
10(9.8)=98
2(9.8)=19.6
Magnitude of 2 kg is ¼ of 10kg vector
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What is the magnitude of the net force on the system as a percent of the largest?
78.4
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You haven't explained how you got this. It isn't clear how the forces you listed lead to this conclusion.
Note that the normal force exerted by the surface is part of the analysis as well.
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Sketch to the same scale the force gravity would exert on the two masses, were combined into one. What is the magnitude of the net force on the system as a percent of this force?
1/6
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I agree with this fraction, which is equal to about 17%.
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`q003. Sketch the force vectors acting on a system of two masses, one of mass 10 kg and the other of 8 kg with the masses suspended on opposite sides by a string over a light frictionless pulley. The tension in the string is considered internal to the system, and the tension pulls each mass toward the other.
How many force vectors did you sketch?
2 vectors
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Identify each of these force vectors and explain what the source of each force is.
Gravity-down
Tension-one mass pulling toward the other
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Gravity exerts forces on each of the masses. So if tension is included there will be at least three forces; however tension is internal to the system and doesn't need to be included here.
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List the vectors in order, from the smallest to the largest.
8
10
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Those look like the masses, absent the units. Easily translated into forces.
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What is the magnitude of each of your vectors, as a percent of the largest?
80%
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The smaller is 80% of the larger. The larger is, of course, 100% of itself.
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What is the magnitude of the net force acting on the system, as a percent of the largest?
4/5
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4/5 would be 80%.
However this isn't correct.
What is your rationale?
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Sketch to the same scale the force gravity would exert on the two masses, were combined into one. What is the magnitude of the net force on the system as a percent of this force?
10x9.8=98
8x9.8=78.4
1/8
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I believe the fraction would be 1/9, which is about 11% of the sum of the magnitudes of the two forces.
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Will the acceleration of the system be greater or less than the acceleration of gravity?
greater
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If you release this system from rest, the 10 kg mass will descend. If at the same time you drop an unattached 10 kg mass from beside the one in the system, it should be clear that the freely falling mass will accelerate at a greater rate than the one attached to the 8 kg mass.
Is this obvious?
Does this affect your answer to the present question?
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`q004. If you were 10 000 km from the center of the Earth, the gravitational attraction between you and the Earth would be (6350 km / (10 000 km) ) ^ 2 times as great as it is on the surface of the Earth (6350 km is the radius of the Earth, so (6350 km / (10 000 km) ) is the inverse ratio of the 10 000 km distance to your distance from the center).
Assume that you and your spacesuit have a mass of 100 kg. What gravitational force would you experience at the 10 000 km distance?
Fgrav=100kgx9.8m/s^2
980Nx.4
400N
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.4 is about right, but you don't say where or how you got that from the given information.
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What would be your acceleration toward the center of the Earth, assuming no other forces to be present?
A=400N/100kg
A=4m/s^2
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If you were in a circular orbit your centripetal acceleration as you move around the circle was equal to the gravitational acceleration you just calculated. The centripetal acceleration of a point moving at speed v around a circle of radius r is v^2 / r. What would be your velocity, were you in a circular orbit?
Acent=v^2/r
V=sqr rt of 40,000kmxm/s^2
4x10^7m2/s^2
6400m/s
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Check my notes and if you do any revisions you want me to see, insert and mark them with &&&&.
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