Question

two hockey players are about to collide on the ice. one player has a mass of 65 kg and is traveling at 1.8 m/s east. the other has a mass of 70 kg and is traveling at 1.4 m/s west. the system consists of the two hockey players.
according to the law of conservation of momentum, what is the total momentum of the system after they collide? assume the collision is an elastic collision.
a. 19 kg·m/s west
b. 19 kg·m/s east
c. 215 kg·m/s west
d. 215 kg·m/s east

Explanation:

Step1: Calculate the initial momentum of each player

• Let east be the positive direction.
• For the first player: \(p_1 = m_1v_1\), where \(m_1 = 65\space kg\) and \(v_1=1.8\space m/s\). So \(p_1 = 65\times1.8= 117\space kg\cdot m/s\)
• For the second player: \(p_2 = m_2v_2\), where \(m_2 = 70\space kg\) and \(v_2=- 1.4\space m/s\) (negative because west is opposite of east). So \(p_2=70\times(-1.4)=-98\space kg\cdot m/s\)

Step2: Calculate the total initial momentum

• According to the law of conservation of momentum \(p_{total - initial}=p_{total - final}\)
• \(p_{total}=p_1 + p_2\)
• \(p_{total}=117+( - 98)=19\space kg\cdot m/s\)

Answer:

B. \(19\space kg\cdot m/s\) east