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A 0.30 kg puck, initially at rest on a frictionless horizontal surface, is struck by a 0.20 kg puck that is initially moving along the x axis with a velocity of 1.9 m/s. After the collision, the 0.20 kg puck has a speed of 0.9 m/s at an angle of θ = 53° to the positive x axis.
It asks me 1. to Determine the velocity of the 0.30 kg puck after the collision.
Which i got, the answer is 1.02 m/s
However when it asks me to Find the fraction of kinetic energy lost in the collision.
so basically i did .5(M1)(V1)^2 subtract .5(m2)(v2)^2.......... it was wrong..
I dunno what to do... I tried doing ((.5(.2m/s)(1.9m/s)^2)) - ((.5)(.3)(1.02)^2)) = .205..... and my answer was wrong... I dunno how to find the kinetic energy lost..
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This kinda does look like your physics teacher to me.
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You are right the total kinetic energy before the collision = (0.5 x 0.2 x (1.9)^2)
but you forgot to include the kinetic energy of the 0.2kg puck when you did you calculation for the total kinetic energy afterwards.
Kinetic energy afterwards = (0.5 x 0.3 x (1.02)^2) + (0.5 x 0.2 x (0.9)^2)
so Kinetic Energy lost is Total KE before - Total KE after
ill let you do the rest.....
Hope i helped
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United States24498 Posts
I got the speed_after for the .3 kg puck should be 1.37 m/s...
The wording for the second part is a bit ambiguous but I think they want you to do...
(Ebefore-Eafter)/Ebefore
If that doesn't work then just try the difference like you were before
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On February 03 2009 11:47 blapsd wrote: You are right the total kinetic energy before the collision = (0.5 x 0.2 x (1.9)^2)
but you forgot to include the kinetic energy of the 0.2kg puck when you did you calculation for the total kinetic energy afterwards.
Kinetic energy afterwards = (0.5 x 0.3 x (1.02)^2) + (0.5 x 0.2 x (0.9)^2)
so Kinetic Energy lost is Total KE before - Total KE after
ill let you do the rest.....
Hope i helped
EDIT: yeah i got 1.37 for speed of 0.3 puck also
this worked thanks
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no problem, you're welcome
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oh HAHA oh ahhhh lol ahahahahah omg stop it hahaha. just wait until you take physics in college . (unless that is college and its some beginner physics :D)
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United States24498 Posts
On February 03 2009 12:02 Hypnosis wrote: oh HAHA oh ahhhh lol ahahahahah omg stop it hahaha. just wait until you take physics in college . (unless that is college and its some beginner physics :D) What the heck is your point?
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He thinks he's hot stuff cuz he took some fancy mathmatics class.
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^^ we must be in the same grade, im doing similar problems.
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United States17042 Posts
On February 03 2009 13:15 Jonoman92 wrote: He thinks he's hot stuff cuz he took some fancy mathmatics class.
except we know that micronesia is king of kings when it comes to this stuff on tl.net xD
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hey i got a problem.. A 1200kg car is traveling at a speed of 25m/s north. It crashes into a truck - 9000kg also moving north at at 70km.h ( which i worked out to be 19.45m/s ). The velocity of the car immediately after the collision was 65km/h North ( which i worked out to be 18.06m/s). Now it asked me what the velocity of the truck was after the collision and i got 20.37m/s north The it asked me to calculate the loss in kinetic energy during the collision... the answer i got was wrong...????
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i used the formula Total KE before - Total KE after (0.5 x (M)(V)^2) + (0.5(M)(V)^2) == that BEING THE FORMULA BEFORE - using the initial velocities and the the same formula for the KE after but using the final velocities. after subtracting the two and i still get the wrong answer.
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Hey what answer did you get? I got something like 14182.5 Joules lost
I didn't round off too accurately so I might be a little out
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On February 03 2009 12:02 Hypnosis wrote: oh HAHA oh ahhhh lol ahahahahah omg stop it hahaha. just wait until you take physics in college . (unless that is college and its some beginner physics :D) Not everyone takes physics in college.
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he just said in a unkind manner that this litle problem will seem like nothing if you ever go to a technical university. i kinda emphasize with hypnosis. It makes me giggle too inside, how i ever found those kinds of problems hard.
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When i look back at the stuff i did in the beginning of the semester i wondered too...
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United States24498 Posts
I took plenty of college physics and I see no point of making fun of people in easier physics classes.
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oh never mind guys .. i got it right. the answer in the book was wrong. Its 14447.04J blapsd
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