Calculating the Change in Kinetic Energy During a Collision

[disruptors]

On a frictionless horizontal air table, puck A (with mass 0.366 kg) is moving toward puck B (with mass 0.254 kg ), which is initially at rest. After the collision, puck A has velocity 0.119 m/s to the left, and puck B has velocity 0.655 m/s to the right.



What was the speed of puck A (Vai) before the collision?

K I put v=v1(m1+m2)/(m1-m2)

v1=-.119 m/s since it moves in the left direction and i defined right as +ve

my initial velocity of puck a came to be -0.659 m/s, but it seems to be wrong.


Calculate , the change in the total kinetic energy of the system that occurs during the collision.

for the KE I got 0.333 J but I don't know why its wrong
thx guys

 

[zoetrope]

K I put v=v1(m1+m2)/(m1-m2)

?

Since puck B is initially at rest, the initial linear momentum of the system is: m1*v

After the collision, the linear momentum will be equal to: m1*v1 + m2*v2

Since linear momentum is conserved, the initial and final linear momentums will be equal. Once you equate these, you can solve for v.

Hope this helps,

zoetrope

 

[disruptors]

yeah that helps thanks

i was looking at it as an inelastic collision

for the energy part i am using the equation

1/2 m1 v1(squared)i = 1/2 m1 v(squared)1f + 1/2 m2 v(squared)2f

question is looking for change in kinetic energy DURING collision

i calculated Final KE - Initial KE but is that not considered the total change in KE DURING the collision?