course phy121 ????????????b??assignment #020
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14:17:41 Explain how we get the components of the resultant of two vectors from the components of the original vectors.
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RESPONSE --> You get the x component of the resulting vector by adding the x components of the original vectors. The y is achieved the same way, using the y components of the origianl vectors. confidence assessment: 3
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14:17:44 ** If we add the x components of the original two vectors we get the x component of the resultant. If we add the y components of the original two vectors we get the y component of the resultant. **
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RESPONSE --> self critique assessment: 3
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14:18:44 Explain how we get the components of a vector from its angle and magnitude.
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RESPONSE --> The x component is the magnitude multiplied by the cosine of the angle: r cos(theta) The y component is the magnitude multiplied by the sine of the angle: r sin(theta) confidence assessment: 3
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14:18:48 ** To get the y component we multiply the magnitude by the sine of the angle of the vector (as measured counterclockwise from the positive x axis). To get the x component we multiply the magnitude by the cosine of the angle of the vector (as measured counterclockwise from the positive x axis). **
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RESPONSE --> self critique assessment: 3
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14:21:41 prin phy, gen phy 7.02. Const frict force of 25 N on a 65 kg skiier for 20 sec; what is change in vel?
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RESPONSE --> Since the force is opposite to the direction of motion, we have an impluse of: -25N * 20sec = -500N sec Momentum = Impulse = m * `dv `dv = impulse / m = -500N sec / 65kg = -7.7m/s confidence assessment: 3
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14:21:53 If the direction of the velocity is taken to be positive, then the directio of the frictional force is negative. A constant frictional force of -25 N for 20 sec delivers an impulse of -25 N * 20 sec = -500 N sec in the direction opposite the velocity. By the impulse-momentum theorem we have impulse = change in momentum, so the change in momentum must be -500 N sec. The change in momentum is m * `dv, so we have m `dv = impulse and `dv = impulse / m = -500 N s / (65 kg) = -7.7 N s / kg = -7.7 kg m/s^2 * s / kg = -7.7 m/s.
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RESPONSE --> self critique assessment: 3
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