Physics: momentum? not homework - i copied this from a book therefore i havent missed anything?

Question

Two particles, of masses x kg and 0.1kg, are moving towards each other in the same straight line collide directly. immediately before the impact, the speeds of the particles are 2ms-1 and 3ms-1 respectively.

a) Given that both particles are brought to rest by the impact, find x?

b) Given instead that the particles move with equal speeds of 1ms-1 after the impact, find the three possible values of x?

Answer 1

Part A)
You need to consider the equation covering the conservation of momentum:
m1.v1+m2.v2 before collision = m1.v1+m2.v2 after collision, bearing in mind that one of the velocities will be negative as the two particles are moving in opposite directions.
m1=X, v1=2
m2=0.1, v2=-3
The final result is two motionless particles, v1=v2=0, so the total momentum is zero, so the sum of the particles' momentum before the collision must also be zero.
X x 2 + 0.1 x -3 = 0
X x 2 = 0.3
X = 0.15kg.

Part B)
The three possibilities are both particles moving one way, both moving the other, or in opposite directions.
Both going 'left', considering left to be the negative velocity direction:
X x 2 + 0.1 x -3 = (X+0.1) x -1
X x 2 - 0.3 = -X - 0.1
X x 3 = 0.2
X = 0.0667kg

Both going 'right':
X x 2 + 0.1 x -3 = (X+0.1) x 1
X x 2 - 0.3 = X + 0.1
X = 0.4kg

Both bouncing off:
X x 2 + 0.1 x -3 = X x -1 + 0.1 x 1
X x 3 = 0.4
X = 0.1333kg

Answer 2

a) since it is inellastic collision therefore only momentum will be conseved there fore
m1v1=m2v2

2x=3*0.1
x=0.15mg