# Inelastic Question HELP

1. Nov 6, 2007

### physicsbhelp

[SOLVED] Inelastic Question HELP!!!!!!!!!!!!!!!!!!

1. The problem statement, all variables and given/known data

A 0.20 kilogram mass is sliding on a horizontal, frictionless air track with a speed of 3.0 meters per second when it instantaneously hits and sticks to a 1.3 kilogram mass initially at rest on the track. The 1.3 kilogram mass is connected to one end of a massless spring, which has a spring constant of 100 Newtons per meter. The other end of the spring is fixed.

A) Determine the following for the 0.20 kilogram mass immediately BEFORE the impact.
1. Its linear momentum:
2. It's kinetic energy:

B) Determine the following for the COMBINED MASSES immediately AFTER the impact.
1. Its linear momentum:
2. It's kinetic energy:

After the collision, the two masses undergo simple harmonic motion about their position at impact.
C) Determine the amplitude of the harmonic motion.
D) Determine the period of the harmonic motion:

2. Nov 6, 2007

### physicsbhelp

OKAY SO THESE ARE THE ANSWERS I GOT FOR ALL OF THEM.
PLEASE TELL ME IF THEY ARE WRONG:

A)
1) 0.6 kg x m/s
2) 0.9 J

B)
1) 4.5 kg x m/s
2) 6.75 J

C) 0.547m
D) o.77s

3. Nov 6, 2007

### physicsbhelp

Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help Help

4. Nov 6, 2007

### Staff: Mentor

Part A is correct. Part B is incorrect.

For part B, momentum must be conserved, but kinetic energy is not since this is an inelastic collision.

See - http://hyperphysics.phy-astr.gsu.edu/hbase/inecol.html

Once the KE for part B is determined, then the deflection of the spring can be determined and that will be the amplitude of the vibration.

For frequency, the should be straightforward knowing k (spring constant) and m.

5. Nov 6, 2007

### physicsbhelp

Thank you, but I still don't get it. I looked at the website and i did what it said but i got the same answers! like i did (m1 + m2)*v and i got 4.5.

also for the kinetic energy in b, i did what the website said but i got the same answer!

6. Nov 6, 2007

### physicsbhelp

1. The problem statement, all variables and given/known data

A 0.20 kilogram mass is sliding on a horizontal, frictionless air track with a speed of 3.0 meters per second when it instantaneously hits and sticks to a 1.3 kilogram mass initially at rest on the track. The 1.3 kilogram mass is connected to one end of a massless spring, which has a spring constant of 100 Newtons per meter. The other end of the spring is fixed.

A) Determine the following for the 0.20 kilogram mass immediately BEFORE the impact.
1. Its linear momentum:
2. It's kinetic energy:

B) Determine the following for the COMBINED MASSES immediately AFTER the impact.
1. Its linear momentum:
2. It's kinetic energy:

After the collision, the two masses undergo simple harmonic motion about their position at impact.
C) Determine the amplitude of the harmonic motion.
D) Determine the period of the harmonic motion:

OKAY SO THESE ARE THE ANSWERS I GOT FOR ALL OF THEM.
PLEASE TELL ME IF THEY ARE WRONG:

A)
1) 0.6 kg x m/s
2) 0.9 J

B)
1) 4.5 kg x m/s
2) 6.75 J

C) 0.547m
D) o.77s

7. Nov 6, 2007

8. Nov 6, 2007

### physicsbhelp

Please I Really Need Help On This.

9. Nov 7, 2007

### Staff: Mentor

One has to apply conservation of momentum in an inelastic collision. One cannot increase the momentum in the collision! The kinetic energy is not conserved.

The combined mass cannot be traveling at the same speed! And it certainly will not increase in speed.

Rather than writing out answers/numbers, please write out one's work, i.e. what forumulas one is using.

10. Nov 7, 2007

### physicsbhelp

thank you astronuc!