# Homework Help: Spring force and frictionless mass vs speed

1. Oct 18, 2014

### wind

1. The problem statement, all variables and given/known data
A mass
(m = 1.35 kg),
originally at rest, sits on a frictionless surface. It is attached to one end of an unstretched spring
(k = 747 N/m),
the other end of which is fixed to a wall (see figure below). The mass is then pushed with a constant force to stretch the spring. As a result, the system (which consists of the wall, spring and mass) comes to a momentary stop after the mass moves 15.0 cm. Find the following.

(e) speed of the mass 4.50 cm into the motion

2. Relevant equations

3. The attempt at a solution
I tried 1/2mv^2 = 1/2K (x1^2-x2^2)
v= sqrt(K ( (0.15^2-0.045^2))/m

not sure how to solve this .. been at it for a while now.

#### Attached Files:

• ###### frictionlesswtf.png
File size:
3.9 KB
Views:
110
2. Oct 18, 2014

### CWatters

I haven't tried to solve it but... when the mass comes to a momentary halt you know all the applied energy is stored in the spring.

3. Oct 18, 2014

### BvU

Hello wind, and welcome to PF.

Your attempt is based on an equation for energy conservation.
You might need another term. How about something that features F ?