A 0.160-kg hockey puck modified to hold +40 C of charge is placed at one end of

Question

A 0.160-kg hockey puck modified to hold +40 C of charge is placed at one end of an ice hockey rink that is 61 m long. At the other end of the rink is a device capable of generating a charge of -0.13 C but only for a short time interval. The coefficient of kinetic friction between ice and puck is k = 0.016. The puck is given a tiny nudge (just enough to get it moving but at a speed of nearly 0, which means you can ignore static friction), and then the charge generator is turned on for 100 ms. Assume the 100-ms time interval is short enough to allow you to assume that the distance between the puck and the charge generator is constant.

What is the puck's speed when it arrives at the generator?

Explanation / Answer

electric force F = k*Q*q/r^2 = 9*10^9*40*10^-6*0.13/61^2 = 12.6 N

acceleration a = F/m

speed of the puck vox = a*t = F*t/m = 12.6*100*10^-3/0.16 = 7.88 m/s

after the generator is turned off

frictional force fk = -uk*m*g = -0.016*0.16*9.8 = -0.0251 N

acceleration ax = fk/m = -( 0.0251)/0.16 = -0.157 m/s^2

vx^2 - vox^2 = 2*ax*x

vx^2 - 7.88^2 = -2*0.157*61

vx = 6.55 m/s

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