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Offlinemilkman
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Physics
    #9878283 - 02/27/09 05:44 PM (5 years, 7 months ago)

I'm having trouble on a few physics question for homework
1.A ball of mass 522g starts at a rest and slides down a frictionless track, as shown(1a). it leaves the track horizontally, striking the ground
a.at what height above the ground does the bal start to move?
b.what is the speed of the ball when it leave the track?
c.what is the speed of the ball when it hits the ground?
1a

for this one i used
[delta]dy=.5g[delta]t*t
assuming g=10m/ss t=.22
with t i now used v=d/t

so c must equal 5.68m/s

im at a loss how to find the rest



dont even know where to start these two

2.Astronaut Melroy, history's third woman space shuttle pilot, flew the shuttle to the ISS to complete the construction in Oct. To undock from the space station pilot melroy released hooks holding the two spaccraft together and the 68,000kg shuttle pushed away from the station with the aid of four large springs.
a.if the 73,000kg space station moved back at a speed of .5m/s how fast and in what direction did the shuttle move?
b.what was the relative speed of the two spacecraft as they separated?



3. In a train yard, train cars are rolled down a long hill in order to link them up with other cars as shown. A car of mass 4000. kg starts to roll from rest at the top of the hill 5.0 m high, and inclined at an angle of 5.0o to the horizontal. The coefficient of rolling friction between the train and the track is 0.050. What velocity would the car have if it linked up with 3 identical cars sitting on flat ground at the bottom of the track? (Hint: The equation for rolling friction is just like the one for sliding friction.)


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InvisibleDieCommie
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Re: Physics [Re: milkman]
    #9878574 - 02/27/09 06:12 PM (5 years, 7 months ago)

For number one use conservation of energy.

For number two use conservation of momentum.

For number three, I believe you should use the work-energy theorem along with conservation of energy.


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Offlinemilkman
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Re: Physics [Re: milkman]
    #9878857 - 02/27/09 06:45 PM (5 years, 7 months ago)


3's solution seems to elude me i cant use KE=.5mv*v i dont have velocity and conservation of energy requires velocity also, im solving for velocity so KE and V would be unknowns, conservation of energy would have velocity initial and velocity final as unknowns


Edited by milkman (02/27/09 07:39 PM)


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InvisibleDieCommie
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Re: Physics [Re: milkman]
    #9879043 - 02/27/09 07:12 PM (5 years, 7 months ago)

For number three you need to consider the work done by friction (work-energy theorem).  The initial potential energy minus the work done by friction is the final kinetic energy.


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Offlinemilkman
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Re: Physics [Re: milkman]
    #9879083 - 02/27/09 07:19 PM (5 years, 7 months ago)

i think i got it but our instructor didn't go over that theorem actually he didnt go over many he just gives us a chapter and goes over the equations on the sheet so we went over KE=PE and such i never saw work energy theorem but thanks

for 2.

a. 0.258m/s
b 0.758m/s

for 3 i got
8.94m/s


i changed my anwser for the ball of mass one
final anwsers
a.3.7m
b. 2m/s
c. 7m/s


Edited by milkman (02/28/09 10:54 AM)


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