3 boxcars moving along frictionless track hits a motionless boxcar

[chaotiiic]

Homework Statement

Three boxcars are rolling along a virtually frictionless track at 20m/s when they strike another boxcar sitting motionless on the track. what is the new speed of the 4 coupled bovcars? all the boxcars have the same mass

Homework Equations

3rd or 2nd Newton law

The Attempt at a Solution

m_a(20) + m_b(20) + m_c(20) + m_d(0) = m_a(v_f) + m_b(v_f) + m_c(v_f) + m_d(v_f)
since all of the masses are equal i cross all of them out.
60 = 4v_f
v_f = 15m/s

 

[PeterO]

Homework Statement

Three boxcars are rolling along a virtually frictionless track at 20m/s when they strike another boxcar sitting motionless on the track. what is the new speed of the 4 coupled bovcars? all the boxcars have the same mass

Homework Equations

3rd or 2nd Newton law

The Attempt at a Solution

m_a(20) + m_b(20) + m_c(20) + m_d(0) = m_a(v_f) + m_b(v_f) + m_c(v_f) + m_d(v_f)
since all of the masses are equal i cross all of them out.
60 = 4v_f
v_f = 15m/s

That is the correct answer to the problem you described.

 

[chaotiiic]

That is the correct answer to the problem you described.

thankyou.