Two objects of the same mass move along the same line in opposite directions. The first mass is moving with speed. The objects collide, stick together, and move with speed 0.100 in the direction of the velocity of the first mass before the collision. What was the speed of the second mass before the collision?

a. 0.00

b. 0.800

c. 0.900

d. 10.0

e. 1.20

Answer: b)

Explanation: In order to explain this problem we first consider that velocity of mass 1 is equal to v. Then we have to considerer that the linear momentum conservation, so:

Pi=Pf

Pi = m*v+m*V2

Pf=2*m*VF where VF is the final velocity for the joined mass and is equal to 0.1*v

then we have;

m*v+m+V2=2*m*0.1*v so

V2=2*0.1*v-v=-0.8*v

V2 is equal to 0.8*v; moving in opposite direction that v.