**An ice hockey puck slides along the ice at ****12**** m/s. A hockey stick delivers an impulse of ****4.0**** kg * m/s causing the puck to move off in the opposite direction with the same speed.**

**What is the mass of the puck?**

Known variables:

initial velocity (v1) : 12 m/s

final velocity (v2) : -12 m/s (opposite direction)

impulse: 4 kg * m/s

**Impulse is the change in momentum**

**Ft** = mv1-mv2

**Ft **= **m**(v1-v2)

4 = **m** [12-(-12)]

**-24m **= 4

Solve for m:

**m **= 1/6 or

**m **= .17 kg

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