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# Answer to Question #18852 in Mechanics | Relativity for Lissah

Question #18852
A 75 kg box slides down a 25.0 degrees ramp with an acceleration of 3.60 m/s/s.find the coefficient of kinetic friction between the box and ramp
1
Expert's answer
2012-11-16T05:17:28-0500
First, you need to find the Force that will impede the moving

Force = Mass * Acceleration
Force = 75kg * 3.60m/s squared
Force = 270 N

Second, find the parallel force ( the force in which it goes up and down )

F(parallel) = Weight * sin(Theta)
Weight = mass * gravity ( you should know this formula by now )

Weight = 75 kg * 9.81 m/ssquared (coef of gravity )
Weight = 735 N

F(parallel) = 735 N * sin(25)
F(parallel) = 310.9 N

Third, you need to find the force due to friction ( the stopping force )

Force of Friction = F(parallel ) - force
Force of friction = 310.9N - 270 N
Force of friction = 41 N

Now, you should use the formula to find the coefficient ( Force of Friction = coef * normal )

To find normal, you need to remember that if the object is moving in an angle, thennormal force = weight * cos 25, if it is moving horizontally, normal force = weight )

So since this is moving in an able,

Normal Force = 735 N * cos(25)
Normal Force = 667N

41 N = Coef * 667N
Coef = 0.061
1 year ago

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#### Comments

Assignment Expert
19.11.12, 14:20

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Lissah
16.11.12, 13:43

Thank you so much !! I totally get it now!!

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