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Two frictionless pucks are placed on a level surface, as shown, at an initial distance of 20 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 m/s [E] and the initial velocity of puck 2 is 8 m/s [W]. Find the minimum separation of the two pucks (the minimum distance between the pucks).

Attempt at the solution:

Let right be positive

Kq1q2/r = 0.5 -m1v1^2 + m2v2^2

9 x 10^9 Nm^2/C^2(3 x 10 ^-4 C) ( 3 x 10^-4 C) /r = 0.5(-0.80)(-12)^2 + (0.40)(8)^2

810Nm^2 / r = 70.4 kgm^2/s^2

r = 11.51m

20 - 11.51 = 8.50m

Is this right?

Attempt at the solution:

Let right be positive

Kq1q2/r = 0.5 -m1v1^2 + m2v2^2

9 x 10^9 Nm^2/C^2(3 x 10 ^-4 C) ( 3 x 10^-4 C) /r = 0.5(-0.80)(-12)^2 + (0.40)(8)^2

810Nm^2 / r = 70.4 kgm^2/s^2

r = 11.51m

20 - 11.51 = 8.50m

Is this right?