Missing sumthing really dumb. Please help?

  • Thread starter mujadeo
  • Start date
  • #1
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Homework Statement



A block of mass M = 3 kg is released from rest and slides down an incline that makes an angle q = 32° with the horizontal. The coefficient of kinetic friction between the block and the incline is µk = 0.15.

What is the acceleration of the block down the inclined plane?


Homework Equations


this is the easiste part of 4 part question and i cant get it.


The Attempt at a Solution


OK heres what i know
Normal = 3kg * (9.8sin32)
so friction is

fs = .15*15.58 = 2.34N
so i'm taking x axis as the incline plane, (pos x = down the plane)
friction opposes the motion, so force runs along neg axis = -2.34N

forces in pos x direction are
3 * 9.8cos32 = 24.93N

24.93N - 2.34N = 22.59N (this is the net force)

Finally F/m = a
22.69/3 = 7.53m/s/s

= wrong.
??

Homework Statement





Homework Equations





The Attempt at a Solution

 
Last edited:

Answers and Replies

  • #2
HallsofIvy
Science Advisor
Homework Helper
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Looks to me like you have sine and cosine reversed. You draw the inclined plane as a right triangle having angle 32 degrees at the bottom. The force of gravity is straight down, the two legs of that triangle are perpendicular and parallel to the inclined plane- the 32 degree angle is the bottom of that triangle. The normal force is given by cos(32), the force along the incline by sin(32).
 
  • #3
103
0
yeah yer right
thanks
 

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