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posted by  Roks203 on 11/6/2009 11:27:02 PM  |  status: Closed  |  Earned Karma: 25

Gravitational Potential Energy

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N/A N/A N/A N/A 11/7/2009 at 12:00:00 PM
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Can someone please explain:
A brick of mass 1.0kg slides down an icy roof inclined at 30 degrees with respect to the horizontal. (a) If the brick starts from rest, how fast is it moving when it reaches the edge of the roof 2.00m away? Ignore friction. (b) Redo part (a) if the coefficient of kinetic friction is 0.10
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Oracle
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posted by D.J84 (MNK) on 11/6/2009 11:40:39 PM  |  status: Live
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Response Details:


m=1 kg
g=9.8 m/s2
N=normal force=m*g*cos30 N

in the first case F=0
net force action=m*g*sin30 N
acceleration=force/mass=(m*g*sin30)/m=g*sin30=4.9 m/s2

initial velocity=u=0
s=2

let velocity after 2m=v
v2=u2+2*a*s
v2=0+2*4.9*2
v=4.43 m/s (ans a)

in the second case
frictional force=F=N*μk=m*g*cos30*0.1=1*9.8*cos30*0.1=0.85 N

net force=m*g*sin30-0.85=1*9.8*sin30-0.85=4.9-0.85=4.05 N
acceleration=force/mass=4.05/1=4.05 m/s2
initial velocity=u=0
final velocity=v

v2=u2+2*a*s
v2=0+2*4.05*2
v=4.02 m/s (ans b)
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