# Hard Problems at least for me help

1. Oct 25, 2006

### allblonde

some other problems if anyone has any ideas

1. the coefficient of static friction between the 3.00 kg crate and the 35 degree incline is .300. What is the magnitude of the minimum force, F, that must be applied to the crate perpendicular to the incline to prevent the crate from sliding down the incline?

: so i know the answer is 32.2 N but im not sure how to get it , do i need to resovle the vectors of gravity(weight)

2.Three blocks are in contact with eachother on a frictionless horizantal surface. A horizantal force, F, is applied to m1 (the first box). For this problem, m1=2kg, m2=3kg, m3=4kg, and F= 180N to the right.
a. find the acceleration of the blocks.
b. find the resultant force on each block.
c. find the magnitude of the contact forces.

2. Oct 25, 2006

### allblonde

i know:
force perpendicular (y) is the force applied*the sin of theta
force parallel (x) is the force applied*the cos of theta
the force due to gravity is the mass*gravity
Fn+Fp-Fg= 0 because the crate is not floating
Fn=-Fp+Fg
Fk=coefficient of friction*Fn
Force perpendicular-Fk=m(a of x)

this is easy to understand and solve when the crate is on a flat horizantal surface, but when i try to plug these things into a problem with an incline, nothing comes out right i dont know if im resolving wrong or what

3. Oct 26, 2006

### xman

Last edited: Oct 26, 2006
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