A 9.0 killogram mass and a 3.0 kg mass are at rest on a frictionless

  • Thread starter scbeturner
  • Start date
  • #1
26
0
1. a 9.0 killogram mass and a 3.0 kg mass are at rest on a frictionless table. A massless spring is compressed between the masses, which are held together by a thread. The thread breaks and the 9.0 kg mass moves to the left with a velocity of 2.0 m/s. Find the velocity of the 3.0 kg mass.



2, m1v1+m2v2=(m1+m2)v3



3. 9(2)+3
18+0=12v3
v3=1.5m/s
this was my original attempt, but i realize it is not solving for the velocity of the 3.0kg mass but i don't know what else to do

Homework Statement





Homework Equations





The Attempt at a Solution

 

Answers and Replies

  • #2
ehild
Homework Helper
15,526
1,901


What does v3 mean?


ehild
 
  • #3
26
0


It stands for the final combined velocity but i am not sure if this equation is right for this problem.
 
  • #4
ehild
Homework Helper
15,526
1,901


No, it is not the final combined velocity. Read the problem: the final velocity of one mass is 2 m/s and you need to find the velocity of the other mass. So there is no combined final velocity. But what do you know about of the initial velocities? Do the masses move?

ehild
 
  • #5
26
0


The masses are initially at rest and then they move in opposite directions
 
  • #6
ehild
Homework Helper
15,526
1,901


The masses are initially at rest and then they move in opposite directions
What is the momentum of the system then?

ehild
 
  • #7
26
0


The force that moves the blocks after the thread breaks?
 
  • #8
PeterO
Homework Helper
2,425
46


1. a 9.0 killogram mass and a 3.0 kg mass are at rest on a frictionless table. A massless spring is compressed between the masses, which are held together by a thread. The thread breaks and the 9.0 kg mass moves to the left with a velocity of 2.0 m/s. Find the velocity of the 3.0 kg mass.



2, m1v1+m2v2=(m1+m2)v3



3. 9(2)+3
18+0=12v3
v3=1.5m/s
this was my original attempt, but i realize it is not solving for the velocity of the 3.0kg mass but i don't know what else to do

Homework Statement





Homework Equations





The Attempt at a Solution



The spring will apply the same sized force on each mass - but opposite in direction.

because the masses are 9kg and 3 kg, the effect of the force on the 3 kg mass will give 3 times the acceleration it causes to the 9kg mass.

That means the 3kg mass will be travelling at 3 times the speed of the 9kg mass at all times.

It sounds like after a while the masses have moved away from the spring. By then the 9 kg mass has accelerated to 2.0 m/s

What do you think that means for the 3 kg mass?
 
  • #9
26
0


That its speed is 6m/s?
 
  • #10
PeterO
Homework Helper
2,425
46
  • #11
26
0


Thank you so much!!:)
 

Related Threads on A 9.0 killogram mass and a 3.0 kg mass are at rest on a frictionless

  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
1
Views
5K
  • Last Post
Replies
3
Views
5K
Replies
1
Views
563
Replies
1
Views
5K
  • Last Post
Replies
10
Views
4K
  • Last Post
Replies
5
Views
3K
Replies
1
Views
12K
Top