- #1
naianator
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Homework Statement
A system consists of two blocks, of masses m and 2m, attached to the ends of a massless spring with a force constant k. The system is placed on a horizontal frictionless surface. Initially, the spring is relaxed. The blocks are then pulled apart an “extra” distance x and simultaneously released from the state of rest.
Find the speed v1 of the block of mass m at the instant the spring is relaxed again. Answer in terms of m, k, and x.
Homework Equations
U_spring = 1/2*k*x^2
K = 1/2*m*v^2
m_1*v_1+m_2*v_2 = m_1*v_1' + m_2*v_2'
The Attempt at a Solution
Momentum is conserved and initially 0 so
m*v_1 = 2m*v_2
and
v_1 = 2v_2
Potential energy in the compressed spring is equal to 1/2*k*x^2 and when the spring reaches equilibrium the potential is 0 and the kinetic energy is equal to 1/2*m*v_1^2+1/2*(2m)*(2v_1)^2 so
1/2*k*x^2 = 1/2*m*v_1^2+4*m*v_1^2
= k*x^2 = m*v_1^2+8*m*v_1^2
= k*x^2 = 9*m*v_1^2
and finally
v_1 = sqrt(k*x^2/(9*m))
Where am I going wrong?