Calculating Final Velocity of Mass 1 in an Elastic Collision

[gneill]

p=mv

So you have p, and you have m...

 

[ScienceGeek24]

hmmm still not 3.59m/s i divided the momentum of px/m=v and it gave me 1.79m/s ...

 

[gneill]

But this is an ellastic collision wouldn't it be vf=(2m/m1+m2)vx and vf=(m1-m2/m1+m2)vy ??

What would vx and vy be in that formula? Both objects are initially moving. That formula might apply if one object was moving and the other stationary.

Conservation of momentum always works.

 

[gneill]

hmmm still not 3.59m/s i divided the momentum of px/m=v and it gave me 1.79m/s ...

The velocity, like momentum, has components. Divide both of the momentum components by m1 to give the components of the velocity. Then, to find the speed, find the magnitude of that vector.

 

[ScienceGeek24]

Got it! Thanks man thankyou for your patience.

 

[gneill]

Got it! Thanks man thankyou for your patience.

No problem. Glad to help. Good luck!

 

[ScienceGeek24]

Wait! on emore thing! I'm trying to find the kinetic energy lost i this one and this is what i did KEf= 1/2(8kg+7kg)(3.52)^2=95.052 j and Ke total= 1/2(8kg)(5m/s)^2+1/2(7kg)(3m/s)^2=131.5 J than i subtracted Ktotal -KEf= 44... something something and that is not he right answer the right asnwer is 86.4J . What did i do wrong??

 

[gneill]

wait! On emore thing! I'm trying to find the kinetic energy lost i this one and this is what i did kef= 1/2(8kg+7kg)(3.52)^2=95.052 j and ke total= 1/2(8kg)(5m/s)^2+1/2(7kg)(3m/s)^2=131.5 j than i subtracted ktotal -kef= 44... Something something and that is not he right answer the right asnwer is 86.4j . What did i do wrong??

Only mass m1 is moving after the collision. Don't sum the masses, they are not stuck together.

KE1 = 131.5 j
KE2 = 45.1 j

KE1 - KE2 = 131 - 45.1 = 86.4 j

 

[ScienceGeek24]

which mas did you get the 45.1 with? because i did 1/2(7kg)(3.56)^2=44.35 not 45.1.

Sorry to take all your time man... :P

 

[ScienceGeek24]

opps never mind got it! Thanks gain man!