course phy201 F˛Ą‰¤źw‰đ…ÝŐµ«ŚüÉ€îě’„‰±ůčOŤassignment #020
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20:32:50 Explain how we get the components of the resultant of two vectors from the components of the original vectors.
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RESPONSE --> Not sure i understand the question fully. But to get the compnents of the final vector from the compnents of other vectors you first add all the X and Y components to get to the two final X and Y components for the vector. confidence assessment: 2
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20:33:16 ** 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 --> ok self critique assessment: 3
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20:34:38 Explain how we get the components of a vector from its angle and magnitude.
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RESPONSE --> The magnitude is the length of the hyp. Knowing this and the angle we can use the sine and cosine funtions of the angle *hyp to get the magnitude of the X and Y components. confidence assessment: 3
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20:34:52 ** 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 --> ok self critique assessment: 3
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20:48:53 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 --> a = F/m so -25N/65Kg = -.38 m/s^2 * 20 sec = -7.6m/s change in velocity confidence assessment: 2
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20:51:57 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 --> I got the right answer but used the laws of motion instead of energy. It's difficult to be sure exactly what is being looked for in any specific assignment. self critique assessment: 2
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21:07:14 gen phy #7.12 23 g bullet 230 m/s 2-kg block emerges at 170 m/s speed of block
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RESPONSE --> the KE lost by the bullet will be transferred to the block. KE before impact is 1/2 * .023kg*(230m/s)^2 = 608 J KE after impact is 1/2*.023kg*(170m/s)^2=332 J dKE = 608 - 332 = 276 J 276 J = 1/2* 2kg*v^2 so v = sqrt of 276 or 16.6 m/s confidence assessment: 2
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21:14:06 **STUDENT SOLUTION: Momentum conservation gives us m1 v1 + m2 v2 = m1 v1' + m2 v2' so if we let v2' = v, we have (.023kg)(230m/s)+(2kg)(0m/s) = (.023kg)(170m/s)+(2kg)(v). Solving for v: (5.29kg m/s)+0 = (3.91 kg m/s)+(2kg)(v) .78kg m/s = 2kg * v v = 1.38 kg m/s / (2 kg) = .69 m/s. INSTRUCTOR COMMENT: It's probably easier to solve for the variable v2 ': Starting with m1 v1 + m2 v2 = m1 v1 ' + m2 v2 ' we add -m1 v1 ' to both sides to get m1 v1 + m2 v2 - m1 v1 ' = m2 v2 ', then multiply both sides by 1 / m2 to get v2 ` = (m1 v1 + m2 v2 - m1 v1 ' ) / m2. Substituting for m1, v1, m2, v2 we will get the result you obtained.**
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RESPONSE --> Why did my method not work? self critique assessment: 1
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