A 2.00 kg block is held in equilibrium on an incline of angle = 70° by a horizon
ID: 1962054 • Letter: A
Question
A 2.00 kg block is held in equilibrium on an incline of angle = 70° by a horizontal force applied in the direction shown in the figure below. If the coefficient of static friction between block and incline is s = 0.300, determine the following.
(a) the minimum value of vector F
_____ N
(b) the normal force exerted by the incline on the block
_____ N
Explanation / Answer
Start by adding all of the forces along the incline.
Fcos-mgsin+Fs=0 (since it is not accelerating)
Now you need to find Fs which is Fs=s*FN
FN is the force of the incline on the object, so add all of the forces perpendicular to the incline.
FN-mgcos-Fsin=0
FN=mgcos+Fsin
So, Fs=s(mgcos+Fsin)
Now plug this into the original equation and you get,
Fcos-mgsin+s(mgcos+Fsin)=0
Fcos-mgsin+smgcos+sFsin=0
Since you are solving for F, keep them both on the left side.
Fcos+sFsin=mgsin-smgcos
F(cos+ssin)=mgsin-smgcos
F=(mgsin-smgcos)/(cos+ssin)
Plug number in and you get,
a.) F=26.3 N
FN was already found earlier to be
FN=mgcos+Fsin
Plugging the answer to a (F=26.3 N) into this equation gives,
b.) FN=31.4 N
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