# Homework Help: Potential and Kinetic Energy

1. Nov 7, 2005

### ledhead86

A 2.00-kg block is pushed against a spring with negligible mass and force constant k = 400 N/m, compressing it 0.220 m. When the block is released, it moves along a frictionless, horizontal surface and then up a frictionless incline with slope of 37 degrees.
Pic
http://community.webshots.com/user/mmaddoxwku"
What is the speed of the block as it slides along the horizontal surface after having left the spring?

Last edited by a moderator: Apr 21, 2017
2. Nov 7, 2005

### Staff: Mentor

If you'd like help, you must show your attempted solution. Hint: Energy is conserved.

3. Nov 7, 2005

### ledhead86

so im thinkin in need to use the formula delta_k=-delta_u. Or k_1+U_1=k_2-K_1. So would K_1= (1/2)(2 kg)(0)^2, and U_1=(1/2)(400 N/m)(0.22 m)^2. k_2=(1/2)(2 kg)*V_2^2, and U_2=(1/2)(400 N/m)(0)^2.

4. Nov 7, 2005

### whozum

Try to express whats going on in words:

When compressed the block has _______ energy and no _____ energy, and when released the ____ energy will be converted into ______ energy because now the block will be moving. Since the sufrace is frictionless the block will move at a _____ velocity having a KE equal to the initially stored _____ energy. It will then lose all this ______ energy to become gravitational _____ energy as it goes up the ramp.

After you fill that out correctly, it should be fairly easy to figure out what is equal to what, and so forth to plug in numbers.

5. Nov 7, 2005

### ledhead86

When compressed the block has potential energy and no kinetic energy, and when released the potential energy will be converted into kinetic energy because now the block will be moving. Since the sufrace is frictionless the block will move at a constant velocity having a KE equal to the initially stored PE energy. It will then lose all this KE energy to become gravitational potential energy as it goes up the ramp.

So I had it setup correctly. Now how do I find how far the block travels up the incline before starting to slide back down ?

6. Nov 7, 2005

### Staff: Mentor

By finding the point where all the energy is transformed to gravitational PE.

7. Nov 7, 2005

### ledhead86

OK. So I know -delta_U=F* D * sin(theta)
So. 9.68=F*D*sin(37). What is F. Is that 400N, the spring constant?

8. Nov 7, 2005

### ledhead86

Never mind, I figured it out.

9. Nov 7, 2005

### whozum

Did the fill inthe blanks help?

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