Question

An 80.0 kg man playing hockey catches a puck moving at 20.0 m/s. The man is initially at rest. The man and puck move together after the collision. The puck's mass is 0.17 kg. What is the final velocity?

Answer 1

using conservation of momentum, the initial momentum of the man is 0, and the puck's is 0.17kg*20m/s=3.4 kg*m/s.  The final mass is 80.17kg.  The final momentum is still p=mv=3.4kg*m/s, so v=3.4/80.17= 0.0424m/s

Answer 2

Answer:

$V_s$=0.0424m/s    

Explanation:

Using the law of the conservation of linear momentum P:

$P_i = P_f$

so:

$M_mV_{mi}+M_pV_{pi} = M_sV_s$

where $M_m$ is the mass of the man, $V_{mi}$ is the initial velocity of the man, $M_p$ is the mass of the puck, $V_{pi}$ is the initial velocity of the puck, $M_s$ is the mass of the puck and the man and $V_s$ is the velocity of both after the collition.

Replacing values, we get:

$(80kg)(0m/s)+(0.17kg)(20m/s) = (80kg + 0.17kg)V_s$

Finally, solving for $V_s$:

$V_s$=0.0424m/s