Calculating Momentum and Mass after a Collision

[hatekhaos]

Homework Statement

The problem states that an object moving at a momentum of 800 m/s( calculated by mass of 80kg x 10 m/s) collides with another object. Both objects are moving forward at 5 m/s. What is the mass of the second object? While moving the objects hit another object moving at 5 m/s in the opposite direction. After the collision they all stop. What is the mass of the 3rd object

Homework Equations

p=m*v

The Attempt at a Solution

For the first part I did Momentum=Mass X Velocity. Since the mass of the first object is known and momentum is conserved I got:
p=m*v
p=m*5
800=m*5
m= 800/5
m=160kg
The mass of the second object is 160kg

Now for the 3rd part where they hit an object and stop. The mass of the 3rd object would need to be the same as the combined mass of object 1 and 2. I cannot figure out the equation for this nor do I know if I am on the right track with the solution from part 2. Of course if that is wrong then the entire solution would be wrong.
Thank you in advance for any guidance.

 

[mfb]

There are units missing.

The mass of the second object is 160kg

Is that really the mass of the second object? After the first collision, both the first and the second object are moving at 5 m/s.

Now for the 3rd part where they hit an object and stop. The mass of the 3rd object would need to be the same as the combined mass of object 1 and 2.

Correct.

I cannot figure out the equation for this

You can solve it similarly to the first collision, but I guess just arguing with symmetry should be fine.

 

[HallsofIvy]

Homework Statement

The problem states that an object moving at a momentum of 800 m/s( calculated by mass of 80kg x 10 m/s)

You mean that the momentum is 800 kg m/s

collides with another object. Both objects are moving forward at 5 m/s. What is the mass of the second object?

While moving the objects hit another object moving at 5 m/s in the opposite direction. After the collision they all stop. What is the mass of the 3rd object

Homework Equations

p=m*v

The Attempt at a Solution

For the first part I did Momentum=Mass X Velocity. Since the mass of the first object is known and momentum is conserved I got:
p=m*v
p=m*5

m*5 is the momentum of the second object only, not the total momentum of both objects. The total momentum of both objects is 80*5+ m*5= 800. Solve for m.

800=m*5
m= 800/5
m=160kg
The mass of the second object is 160kg

Now for the 3rd part where they hit an object and stop. The mass of the 3rd object would need to be the same as the combined mass of object 1 and 2. I cannot figure out the equation for this nor do I know if I am on the right track with the solution from part 2. Of course if that is wrong then the entire solution would be wrong.
Thank you in advance for any guidance.

The total momentum of the first two masses is, from above 800 kg m/s. Taking the mass of the third object to be M, its momentum is -5M kg m/s so the total momentum, before the collision is 800- 5M kg m/s. After the collision they are stopped so the total momentum is 0.
800- 5M= 0. Solve for M.

 

[hatekhaos]

Thank you for the help!