Kinematics Question. Incline, Spring, Friction

  • #1
32
1

Homework Statement


Practice problem for midterm.
mKq3pH6.png


Homework Equations


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


The Attempt at a Solution


[/B]
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.
 

Answers and Replies

  • #2
Simon Bridge
Science Advisor
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hint: work against friction.
 
  • #3
gneill
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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
32
1
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
gneill
Mentor
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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?
 

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