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course Phy 121
A simple pendulum has length 2 meters. It is pulled back 10 cm from its equilibrium position and released. The tension in the string is 5 Newtons. •Sketch the system with the pendulum mass at the origin and the x axis horizontal.
answer/question/discussion:
The y axis would represent the length in meters. The x axis would represent the distance from equilibrium in centimeters.
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• Sketch a vector representing the direction of the pendulum string at this instant. As measured from a horizontal x axis, what is the direction of this vector? (Hint: The y component of this vector is practically the same as the length; you are given distance of the pullback in the x direction. So you know the x and y components of the vector.)
answer/question/discussion:
The vector would appear in the lower right quadrant of the graph. So at 280 degrees.
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• What is the direction of the tension force exerted on the mass?
answer/question/discussion:
The tension would be pulling down on the string and back to equilibrium.
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• What therefore are the horizontal and vertical components of the tension?
answer/question/discussion:
Rx = 5 N cos 280 degrees = 0.87
Ry = 5 N sin 280 degrees = -4.9
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• What therefore is the weight of the pendulum, and what it its mass?
answer/question/discussion:
5 N
5 kg m/s^2 /(9.8 m/s^2 * 2 meters) = 2.55 kg m
I am missing the Joules. I feel like I have to make the N become J. From this I would be able to obtain mass and weight.
The weight is m g. So the mass it weight / g (i.e., m g / g gives you m). The 2 meters doesn't come into this calculation.
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• What is its acceleration at this instant?
answer/question/discussion:
I think that this would follow in sync with the last problem.
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