Explanation:
Let us assume that the direction in which Al is moving is in positive direction. The, according to the law of conservation of linear momentum the equation will be as follows.
[tex](m \times (0 m/s) + (168 kg - m)(0 m/s) = m \times (0.90 m/s) + (168 kg - m)(-1.2 m/s)[/tex]
0 = [tex]m \times (0.90 m/s) - (168 kg)(1.2 m/s) + m(1.2 m/s)[/tex]
m = [tex]\frac{168 kg \times 1.2 m/s}{0.90 m/s + 1.2 m/s}[/tex]
= 96 kg
Thus, we can conclude that mass of Al's is 96 g.