- #1
Dustinsfl
- 2,281
- 5
Homework Statement
A hammer strikes an anvil with a velocity of 50ft/sec. The hammer weights 12 lb and the anvil weighs 100 lb. The anvil is supported on four springs with k = 100 lb/in. Find the motion if
(a) the hammer stays in contact with the anvil
(b) the hammer doesn't remain in contatct
Homework Equations
##1 lb = 4.45 N##
##1 m = 3.28ft##
##k_{eq} = 4k = 400\cdot 4.45\cdot 12\cdot 3.28 = 70060.8## N/m
##W = mg## so ##m_h = 12*4.45/9.8 = 5.45## kg and ##m_a = 100*4.45/9.8 = 45.41## kg
##\dot{x}(0) = 50/3.28 = 15.24## m/s
The Attempt at a Solution
(a)
$$
M\ddot{x} + k_{eq}x = 0
$$
where ##M = m_h + m_a = 50.86## kg.
$$
\ddot{x} + \omega_n^2x = 0
$$
where ##\omega_n^2 = \frac{70060.8}{50.86} = 1377.52##
Let ##x(t) = A\cos(\omega_nt) + B\sin(\omega_nt)##. Then ##\ddot{x} = -A\omega_n^2\cos(\omega_nt) - B\omega_n^2\sin(\omega_nt)##.
$$
\cos(\omega_nt)[-A\omega_n^2 + A\omega_n^2] + \sin(\omega_nt)[-B\omega_n^2 + B\omega_n^2] = 0
$$
The coefficient zero out so this can't be correct. The RHS has to be zero since there is no driving force.
Last edited: