Spring Constants problem at the High School level

[jamesgunn]

Homework Statement

A 200N/m spring is compressed 4cm and is used to launch a 0.2kg ball horizontally. How fast is the ball going when the spring has moved 3cm? How fast does the ball leave the cannon?

Relevant Equations

1/2 kx^2=mgh ?

1/2 kx^2 = mgh

 

[hutchphd]

The spring energy goes to Kinetic Energy .

 

[jamesgunn]

The spring energy goes to Kinetic Energy .

Does that mean I use the same formula? You lost me.

 

[Steve4Physics]

The question tells you the motion is horizontal. So what happens to the gravitational potential energy?

Do you you know the formula for kinetic energy?

 

[jamesgunn]

The question tells you the motion is horizontal. So what happens to the gravitational potential energy?

Do you you know the formula for kinetic energy?

No, I could really use some help. I've been doing this problem for the past hour.

 

[Steve4Physics]

Kine

No, I could really use some help. I've been doing this problem for the past hour.

Kinetic energy is $\frac{1}{2}mv^2$
It's one of the most important formulae in basic physics!

 

[jamesgunn]

Kine

Kinetic energy is $\frac{1}{2}mv^2$
It's one of the most important formulae in basic physics!

Ok, I do know that actually. How do I apply this to get the speed for the ball though?

 

[Steve4Physics]

Ok, I do know that actually. How do I apply this to get the speed for the ball though?

Q1.What is the energy stored in the spring when its compression = 4cm?

Q2. When the spring has moved 3cm, how big is its compression now? And how much energy is in the spring now?

Q3. What is the difference in the answers to Q1 and Q2? What has happened to some of the spring's energy?

 

[kuruman]

You use mechanical energy conservation. You say kinetic + potential energy at point A is equal to kinetic + potential energy at point B. What points does it make sense to choose as A and B? Read the problem and see what you know and what you are looking for.

 

[berkeman]

@jamesgunn -- please show some effort, or you thread will be closed. Thank you.