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[H]Physics HALP

Blogs > YPang
Post a Reply
1 2 Next All
YPang
Profile Blog Joined April 2007
United States4024 Posts
Last Edited: 2009-02-03 02:34:44
February 03 2009 02:31 GMT
#1
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..

*
sMi.Gladstone | BW: B high| SC2: gold T_T
Hittegods
Profile Joined April 2007
Stockholm4641 Posts
February 03 2009 02:33 GMT
#2
This kinda does look like your physics teacher to me.
This neo violence, pure self defiance
blapsd
Profile Blog Joined January 2009
England121 Posts
Last Edited: 2009-02-05 22:17:41
February 03 2009 02:47 GMT
#3
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
micronesia
Profile Blog Joined July 2006
United States24753 Posts
February 03 2009 02:49 GMT
#4
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
ModeratorThere are animal crackers for people and there are people crackers for animals.
YPang
Profile Blog Joined April 2007
United States4024 Posts
February 03 2009 03:01 GMT
#5
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
sMi.Gladstone | BW: B high| SC2: gold T_T
blapsd
Profile Blog Joined January 2009
England121 Posts
February 03 2009 03:02 GMT
#6
no problem, you're welcome
Hypnosis
Profile Blog Joined October 2007
United States2061 Posts
Last Edited: 2009-02-03 03:02:40
February 03 2009 03:02 GMT
#7
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)
Science without religion is lame, Religion without science is blind
ilovehnk
Profile Joined October 2008
475 Posts
February 03 2009 03:19 GMT
#8
good old physics
Hikou Shinketsushuu
micronesia
Profile Blog Joined July 2006
United States24753 Posts
February 03 2009 03:20 GMT
#9
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?
ModeratorThere are animal crackers for people and there are people crackers for animals.
Jonoman92
Profile Blog Joined September 2006
United States9106 Posts
February 03 2009 04:15 GMT
#10
He thinks he's hot stuff cuz he took some fancy mathmatics class.
imperfect
Profile Blog Joined July 2008
Canada1652 Posts
February 03 2009 04:52 GMT
#11
^^ we must be in the same grade, im doing similar problems.
blind bisu free and anytime fanboy.
GHOSTCLAW
Profile Blog Joined February 2008
United States17042 Posts
February 03 2009 08:22 GMT
#12
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
PhotographerLiquipedia. Drop me a pm if you've got questions/need help.
g girl
Profile Joined February 2009
South Africa4 Posts
February 05 2009 15:31 GMT
#13
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...????
g girl
Profile Joined February 2009
South Africa4 Posts
February 05 2009 15:37 GMT
#14
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.
blapsd
Profile Blog Joined January 2009
England121 Posts
February 05 2009 16:44 GMT
#15
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
Klockan3
Profile Blog Joined July 2007
Sweden2866 Posts
February 05 2009 19:52 GMT
#16
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.
Marradron
Profile Blog Joined January 2009
Netherlands1586 Posts
February 05 2009 21:53 GMT
#17
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.
YPang
Profile Blog Joined April 2007
United States4024 Posts
February 05 2009 23:25 GMT
#18
When i look back at the stuff i did in the beginning of the semester i wondered too...
sMi.Gladstone | BW: B high| SC2: gold T_T
micronesia
Profile Blog Joined July 2006
United States24753 Posts
February 05 2009 23:39 GMT
#19
I took plenty of college physics and I see no point of making fun of people in easier physics classes.
ModeratorThere are animal crackers for people and there are people crackers for animals.
g girl
Profile Joined February 2009
South Africa4 Posts
February 09 2009 19:34 GMT
#20
oh never mind guys .. i got it right. the answer in the book was wrong. Its 14447.04J blapsd
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