Question

Two objects that are moving in the $xy$ plane on a frictionless floor collide head on. Assume that they form a closed isolated system. The following table gives the momentum components in $\text{kg m/s}$ before and after the collision. What are the missing values $(a,b)$ (in $\text{kg m/s}$)?
$$\begin{array}{ccccc}& \text{Before collision}& & \text{After collision}& \\ \text{Object}& P_x& P_y& P_x& P_y\\ A& -4& 5& 3& a\\ B& b& -2& 4& 2\end{array}$$

• A. $11,1$
• B. $10,11$
• C. $5,7$
• D. $1,11$

Answer 1

The correct option is D $1,11$

Applying momentum conservation in $x$ direction.
$\sum P_x$ (before collision) $=\sum P_x$ (after collision)
$-4+b=3+4\Rightarrow b=11$

Now, in $Y$ direction
$\sum P_y$ (before collision) = $\sum P_y$ (after collision)
$5-2=a+2\Rightarrow a=1$