A 0.17 kg hockey puck has a velocity of 2.4 m/s toward the east (the + x directi
ID: 1319007 • Letter: A
Question
A 0.17 kg hockey puck has a velocity of 2.4 m/s toward the east (the +x direction) as it slides over the frictionless surface of an ice hockey rink. What are the (a) magnitude and (b) direction of the constant net force that must act on the puck during a 0.30 s time interval to change the puck's velocity to 4.9 m/s toward the west? What are the (c) magnitude and (d) direction if, instead, the velocity is changed to 4.9 m/s toward the south? Give your directions as positive (counterclockwise) angles measured from the +x direction.
Explanation / Answer
initial velocity = 2.4i m/s
final velocity = -4.9i m/s
Impulse = change in momentum = 0.17 ( -4.9i - 2.4i) = -1.24i kg.m/s
Impulse = F x t
-1.24 i = F x 0.30
F = - 4.14i N
a) magnitude = 4.14 N
b) direction = west
if final velocity v = -4.9j
Impulse = 0.17 ( -4.9j - 2.4i)
F x t = impulse
F = 0.17 ( -4.9j - 2.4i) / 0.30 = - 1.36i - 2.78 j N
c) magnitude = sqrt(1.36^2 + 2.78^2) =3.09 N
d) direction = 180 + tan-1(2.78/1.36) = 243.93 degrees
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