- #1

Jaimie

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## Homework Statement

"Two frictionless pucks are placed on a level surface at an initial distance of 20.0 m. The mass of puck 1 is 0.80 kg and it has a charge of +3.0 X 10^-4 C., while puck 2 is 0.40 kg with a charge of +3.0 X 10^-4 C. the initial velocity of puck 1 is 12.0 m/s (E) and the initial velocity of puck 2 is 8.0 m/s (W). Find the minimum separation of the two pucks."

## Homework Equations

Pti= Ptf

Etki= Etkf+ Ee

## The Attempt at a Solution

(I dropped the units just so reads easier)

m1v1+m2(-v2)=(m1+m2)vf

vf=(0.80)(12)+(0.40)(-8)/0.80+0.40

vf=5.33 m/s

Ek1+Ek2=Ee+Ekf

1/2m1v1^2 + 1/2m2(-v2^2) = kq^2/r + 1/2(m1+m2)(v')^2

1/2(0.80)(12)^2 + 1/2(0.40)(-8.0)^2 = 1/2(0.80+0.40)(5.33)^2+(9.0X10^9)(+3.0X10^-4)^2/r

Isolate for r

r= 1/2(0.40)(-8.0)^2= 15.2 m= 15m

Can someone advise if this is correct? I am unsure about this answer as it isn't that different from the original distance. In a similar example (as per homework manual), it is taking the initial electric potential energy as negligible. Is this right?