# Homework Help: Simple pendulums

1. Apr 7, 2010

### cdotter

1. The problem statement, all variables and given/known data
A 2.00-kg frictionless block is attached to an ideal spring with force constant 300 N/m. At t=0 the spring is neither stretched nor compressed and the block is moving in the negative direction at 12.0 m/s. Find the amplitude and the phase angle.

2. Relevant equations
x=A*cos(ωt+φ)
v=-ωA*sin(ωt+φ)
$$\omega = \sqrt{\frac{k}{m}}$$

3. The attempt at a solution

$$\omega = \sqrt{\frac{300}{2.00}} = 12.25$$
$$0 = A\cdot cos(\phi)$$
$$12.0 = -12.25 \cdot A \cdot sin(\phi)$$

How do I solve for something when there are two unknowns (phi and A)?

2. Apr 7, 2010

### cdotter

Do I assume that A is non-zero, therefore making φ = Pi/2 radians?