it is acceleration question, help me!!?
“A crate slides down an incline that is 39o above the horizontal. The coefficient of friction between the crate and the plane is μ = 0.68. Find the acceleration of the crate”
I solved that it was -0.989 m/s^2 but it was wrong. isn’t it negative acceleration? anyway, can anybody know this? please help me
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♦ balance of forces and 2nd Newton law: net force F=m*a, where F=f1-f2, f1=mg*sin39° is the component of weight of crate along the incline down,
f2=μ*mg*cos39° is braking force due to component of weight of crate, normal to the incline; Thus
♥ mg*(sin39 – μ*cos39) = m*a, hence
a=g*( sin39 – 0.68*cos39)=0.988 m/s^2; ok!
Naturally ‘a’ is directed along the plane down; so it is not wrong!
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I don’t know much about this stuff, but if the crate is sliding downhill, it can’t be negative acceleration, can it? I mean… it should be speeding up right?… ?? ? …
I really don’t know tho…
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Your quessie is darn difficult.
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