Query22

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course Phy 231

7/6/12 @ 9:51am

If your solution to stated problem does not match the given solution, you should self-critique per instructions at http://vhcc2.vhcc.edu/dsmith/geninfo/labrynth_created_fall_05/levl1_22/levl2_81/file3_259.htm.

Your solution, attempt at solution. If you are unable to attempt a solution, give a phrase-by-phrase interpretation of the problem along with a statement of what you do or do not understand about it. This response should be given, based on the work you did in completing the assignment, before you look at the given solution.

022. `query 22

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Question: `qQuery gen phy 7.19 95 kg fullback 4 m/s east stopped in .75 s by tackler due west

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Your solution:

The equation, p = m * v1 is used to obtain, 115kg (4m/s) = 380 kg m/s. The impulse is then found by pFinal - pInitial , 0 kg m/s - 380 kg m/s = -380 kg m/s. Since the impulse is negative, it is going West. To find Fave, the equation, 'dp / 'dt is used to obtain, -380 kg m/s /(.75s) = -506 N, Fave is also negative so it is in the West direction. Since we were told that the force on the tackler is the same and opposite then the force on the fullback, the force on the tackler is 506 N. Since it is positive, the impulse goes Eastward.

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Given Solution:

`a** We'll take East to be the positive direction.

The original magnitude and direction of the momentum of the fullback is

p = m * v1 = 115kg (4m/s) = 380 kg m/s. Since velocity is in the positive x direction the momentum is in the positive x direction, i.e., East.

The magnitude and direction of the impulse exerted on the fullback will therefore be

impulse = change in momentum or

impulse = pFinal - pInitial = 0 kg m/s - 380 kg m/s = -380 kg m/s.

Impulse is negative so the direction is in the negative x direction, i.e., West.

Impulse = Fave * `dt so Fave = impulse / `dt. Thus the average force exerted on the fullback is

Fave = 'dp / 'dt = -380 kg m/s /(.75s) = -506 N

The direction is in the negative x direction, i.e., West.

The force exerted on the tackler is equal and opposite to the force exerted on the fullback. The force on the tackler is therefore + 506 N.

The positive force is consistent with the fact that the tackler's momentum change in positive (starts with negative, i.e., Westward, momentum and ends up with momentum 0).

The impulse on the tackler is to the East. **

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