# Kinematics Question. Incline, Spring, Friction

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1. Oct 27, 2014

### dmoney123

1. The problem statement, all variables and given/known data
Practice problem for midterm.

2. Relevant equations

T_1+U_1=T_2+U_2
U_spring=1/2kx^2

3. The attempt at a solution

Set X-axis along the 30 degree line and the Y-axis perpendicular.

I'm not sure how to consider the friction constant into the formula.

Any help is very much appreciated.

2. Oct 27, 2014

### Simon Bridge

hint: work against friction.

3. Oct 27, 2014

### Staff: Mentor

Calculate the friction forces (static and kinetic). Make sure the block can move when released (static friction). If the block moves against friction (kinetic friction), what work is done? What happens to the energy involved in friction?

4. Oct 28, 2014

### dmoney123

sumF_y=0
N-mgcos30=0
N=17 N

sumF_x=0
F_spring-F_friction=m_block*accel_block
kx-uN=ma

if static, accel=0

410(0.5)-u(17)=0
u=12.06

doesnt seem right... i think the x is wrong for the spring but i can't visualize it.

5. Oct 28, 2014

### Staff: Mentor

You want to compare the spring force with the static friction force. What must the relationship be if the block is to be able to move from rest?