- #1
SeventeenForever
Homework Statement
[/B]A block of mass, m, is dropped from height, h (above the plate), onto a plate of mass, M, which is attached to a spring with spring constant, k. The block sticks to the plate and the system starts to oscillate. What is the amplitude of the oscillations.
Homework Equations
Etotal=K + Ugravitational + Uspring
Uspring=0.5kx2
K=0.5mv2
Ugravitational=mgh
Conservation of Energy
The Attempt at a Solution
I decided to approach this problem from an energy perspective, setting the equilibrium position of the spring (w/ plate) as 0 gravitational potential energy.
The initial gravitational potential energy is Ug=mgh. Just before it hits the plate, all of this gravitational PE is converted to KE.
mgh = 0.5mv2
v= (2gh)0.5
The problem specifically states that the block "sticks" to the plate, suggesting a completely inelastic collision. I can use the conservation of momentum to find the velocity after the collision; after the collision, the velocity of the plate and block is:
vf= m(2gh)0.5 / (m+M)
The kinetic energy of the system is now:
0.5(m+M)vf2 = Kf
The spring will then be compressed from its equilibrium position until the velocity of the plate/block becomes zero, which is the max compression/amplitude. At this point, all of the kinetic energy has been converted to elastic potential energy.
0.5(m+M)vf2 = 0.5kx2
I can then plug in my equation for vf and solve for x, which is the maximum compression/amplitude.
Is this approach okay? Did I make any incorrect assumptions?
Thaaaaaanks!