Center of Mass Identical Size Object Connected by Spring

[Crazynutjob]

Homework Statement

Two identical 0.19 kg blocks (labeled 1 and 2) are initially at rest on a nearly frictionless surface, connected by an unstretched spring, as shown in the upper diagram, where x2 = 0.05 m. Then a constant force of 8 N to the right is applied to block 2, and at a later time the blocks are in the new positions shown in the lower diagram, where x1 = 0.01 m and x3 = 0.12 m. At this final time, the system is moving to the right and also vibrating, and the spring is stretched.

http://www.webassign.net/mi3/09-056-two_blocks_and_spring.jpg
http://www.webassign.net/mi3/09-056-two_blocks_and_spring.jpg

Homework Equations

What is the final location of the center of mass of the real system?
xCM,final =



POINT PARTICLE SYSTEM
What is the initial location of the point particle system?

The Attempt at a Solution

I tried (x3 -x1)/2 = (.12- .01)/2 = 0.055 m
this is incorrect according to web assign

what am i doing wrong.

 

[Andrew Mason]

Homework Statement

Two identical 0.19 kg blocks (labeled 1 and 2) are initially at rest on a nearly frictionless surface, connected by an unstretched spring, as shown in the upper diagram, where x2 = 0.05 m. Then a constant force of 8 N to the right is applied to block 2, and at a later time the blocks are in the new positions shown in the lower diagram, where x1 = 0.01 m and x3 = 0.12 m. At this final time, the system is moving to the right and also vibrating, and the spring is stretched.

http://www.webassign.net/mi3/09-056-two_blocks_and_spring.jpg
http://www.webassign.net/mi3/09-056-two_blocks_and_spring.jpg

The Attempt at a Solution

I tried (x3 -x1)/2 = (.12- .01)/2 = 0.055 m
this is incorrect according to web assign

what am i doing wrong.

Perhaps you could explain your reasoning. I am not sure that the problem is fully explained. Is the "final" position supposed to represent the maximum stretch of the spring?

What is the force on block 1 (hint: you have to assume a spring constant k)? How does the acceleration of block 1 affect the acceleration of Block 2?

AM

 

[TimmyD]

xcm = (m1x1 + m2x2)/(m1+m2)