# Pendulum/Simple Harmonic Motion, what is its energy of motion?

1. Nov 16, 2011

### nicoleb14

A 1.2 kg mass attached to a spring oscillates with an amplitude of 5.1 cm and a frequency of 2.1 Hz. What is its energy of motion?

I just have to use KE=1/2mv^2 right?
do I have to involve the amplitude?

2. Nov 16, 2011

### grzz

In SHM the KE is continually varying. So you are asking for the MAX KE, right?

3. Nov 16, 2011

### nicoleb14

I just need the energy of motion, so i guess that means KE max?

4. Nov 16, 2011

### technician

The KE max will be the total energy of the motion.
You are correct to use KE=1/2mv^2 but you need an expression for vmax in simple harmonic motion. You will need to find the spring constant (stiffness) and use this to find the max velocity.
Do you know these equations?

5. Nov 16, 2011

### grzz

What is the max linear velocity in SHM?

6. Nov 16, 2011

### nicoleb14

Vmax=Aw

7. Nov 16, 2011

### grzz

Then you can find max ke = (1/2)mv^2 and use v = Aw

8. Nov 16, 2011

### nicoleb14

thank you sooo muuuch!!!!! :D

9. Nov 16, 2011

### PeterO

Is this mass hanging from the spring, or is this whole situation taking place horizontally??

10. Nov 16, 2011

### nicoleb14

the problem doesnt say

11. Nov 16, 2011

### PeterO

Assuming it is vertical, there is a constant interchange of elastic energy in the spring, gravitational potential energy and kinetic energy.

The total of them at any time will be constant.

That might be what is meant by the energy of the motion.

Even if the situation is horizontal [so no change in gravitational potential energy] there is a steady interchange between elastic potential energy and kinetic energy.