sammeh13 (2012-07-13 21:31:07)

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I don't know Physics. Why do I want kniw them? They seem fun. Dx Urm..

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Junaid (2012-07-13 22:01:36)

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\/ Physics.

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1) C.
Momentum is mass multiplied by velocity.
Since you are looking for the momentum imparted on the gun, you use the bullet to find momentum. Since the velocity is the same but bullet 1 is 2x heavier than bullet 2, then the momentum imparted on gun 1 is 2x that of gun 2
Therefore 2:1

2) E.
In elastic collision, both kinetic energy and momentum are conserved. In an elastic collision between two bodies of equal masses, the velocities get exchanged. Since the second body initially was at rest, after collision, the first body comes to rest transferring 100% of its kinetic energy to the second body.

3) I think it's something like this:
vf = vo+a*t
vf = 0+2*4
vf = 8 m/s
d = 4*8 < constant velocity distance = 32
d_acceleration = v0*t+1/2*a*t^2=1*4^2=16
total d = 48
48/4 = 12 poles
d=2*4 = 8 = 2 more poles
= 14 poles

4)
5 nickels = 5*5.7gm = 28.5 gm
4 pennies = 4*2.5 = 10.0 gm
Total mass = 38.5gm
Mid mass = 19.15gm
5 nickels at bottom weigh = 28.5gm.
19.15/5.7 = 3.36 = nickel height. This will be equal to 3.36*1.9 = 6.38mm.
The centre of mass will be at the height 6.38mm when nickels are stacked first.

I may be wrong about some of these.

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Junaid (2012-07-13 22:12:57)

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This is a long way to answer question 3.

During acceleration,
x = xo + vo t + 1/2 at^2
x = 0m + (0m/s)(4s) + 1/2 (2 m/s^2)(4s)^2
x = 16 m

During constant velocity,
a = (vf - vo)/t
2 = (v - 0)/4
v = 8 m/s

x = vo t
x = 8 * 4
x = 32 m

During deceleration,
a = (vf - vo)/t
a = (0 - 8)/2
a = -4 m/s^2

x = xo + vo t + 1/2 at^2
x = 0m + (8 m/s)(2s) + 1/2(-4 m/s^2)(2s)^2
x = 16 - 8
x = 8

Total distance:
16 + 32 + 8 = 56
56 / 4 = 14 poles

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Shy (2012-07-13 22:14:03)

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Juny. Y U SO SMART.

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Junaid (2012-07-13 23:02:33)

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It is the actual formula which is given in your book:
L = I*W + m*v*r

If you want to find the angular momentum about the centre of the disc , then r=0

So the formula becomes:
L = I*W

But in your question you have have to find L about the origin so r can't be 0 because it is at some distance from the origin.

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