Asst_20_query

course Phy 121

J֬De⺉[Ђassignment #020

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ŝInUᾗWʙw

Physics I

07-08-2006

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11:14:48

Explain how we get the components of the resultant of two vectors from the components of the original vectors.

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We take the inverse tangent of the ycomponent divided by the x component.

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11:15:13

** 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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Oh, I guess I didn't understand the question

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11:17:03

Explain how we get the components of a vector from its angle and magnitude.

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For the x component we must take Fcos(theta)

fir y we take Fsin(theta)

We can always find the hypoteneuse by using the Pythagorean theorem.

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11:17:14

** 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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OK

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11:51:38

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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11:54:11

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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Your work on this assignment is good, but note that you should have responded to the prin phy/gen phy problem. Let me know if you have questions.