The force of friction moving up a slope

[tyler24_11]

A grocery cart is being pushed with a force of 450 N at an angle of 30.0 degrees to the horizontal. If the mass of the groceries is 42 Kg,
(a) Calaculate the force of friction if the coefficient is 0.60.

Alright guys I have been doing this problem for around two hours. My physics teacher isn't a good teacher and I have no idea how to get the right answer(located in the back of book).Ive tried all I can think of,
Ff= (0.60)(450n)
= 270n

450 COS 30
= 389.7 N
and a bunch of othe stuff I erased off my paper

The answer in the back is 3.8 x 102 or around 380 n

 

[Integral]

What is the mass of the cart and groceries?

 

[tyler24_11]

it doesn't say just assume 42kg I geuss

 

[LowlyPion]

it doesn't say just assume 42kg I geuss

The 450 N force has 2 components. There is the Cos30 component forward, but there is also the Sin30 component down. Sin30*450 N + 42*(9.8) N = 225 + 411.6 N = 636.6 N in the downward direction.

Then you use your coefficient of friction based on the total downward force.

 

[tyler24_11]

yah, thanks. I figured it out last night. I drew a diagram