A hockey puck has a velocity of v = v x i + v y j . Another puck with identical

Question

A hockey puck has a velocity of v = vxi + vyj. Another puck with identical mass is at rest at the origin. The two pucks collide. After the collision it is observed that the second puck has a velocity of vf = v2yj.

vx = 4.9 m/s
vy = 4.5 m/s
v2y = 1.35 m/s

a)write an expression for the first puck's velocity, in terms of the problem's variables and i and j.

b)what is the magnitude of the first puck's velocity in m per s after the collision?

c)At what angle does this velocity make with respect with the x-axis?

Explanation / Answer

a.

Momentum conservation can be applied here.

Since the masses are equal, velocities can directly be conserved.

Let the final velocity of puck 1 is, vx1i+ vy1j

Conservation:

Vxi + Vyj + 0 = Vx1i +Vy1j + v2yj

=> 4.9i + 4.5j = vx1i + vy1j + 1.35j

=> 4.9 = vx1 and 3.15 = vy1

=> v = [4.9i + 3.15j] m/s

b.

Magnitude = [4.9 + 3.15] 1/2 = 5.825 m/s

c.

Theta = tan-1 (3.15/4.9) = 32.7o

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