Question

Running at 2.0 m/s, Marty, the 45.0-kg quarterback, collides with Biff, the 90.0-kg tackle, who is traveling at 7.0 m/s in the other direction. Upon collision, Biff continues to travel forward at 1.0 m/s. How fast is Marty knocked backwards?

Answer 1

10 m/s backward

Explanation:

We have that for the change of momentum, the following formula:

`m_1\cdot v_(11)+m_2\cdot v_(12)=m_1\cdot v_(12)+m_2\cdot v_(22)`

We substitute, the known values, to calculate the value of Marty's velocity:

`\begin{gathered} 45\cdot-2+90\cdot7=45\cdot-v_(12)+90\cdot1 \\ v_(12)=(45\cdot-2+90\cdot7-90\cdot1)/(-45) \\ v_(12)=(-90+630-90)/(-45) \\ v_(12)=(450)/(-45) \\ v_(12)=-10\text{ m/s} \end{gathered}`

Therefore, Marty's velocity is 10 m/s backward.