Calculate Acceleration of Crate w/ Friction - 1930N, 408kg, 0.26u

[lolkbye]

1. A crate is pushed horizontally with a force.
The acceleration of gravity is 9.8 m/s2 .
Calculate the acceleration of the crate.
Answer in units of m/s2

force=1930 N
mass=408 Kg
friction acting on crate=0.26



2. f=ma
u=fk/fn



3. what is the difference between fk and u(friction)? I don't know where to start! :(

 

[tatiana]

you need to start with drawing a free body diagram for what you have, after that yuo will be able to see what you have and plug it into the equations that you have.. an i believe that because you are moving horizontally not vertically that acceleration of gravity it unnecessary.. but try drawing an FBD first an see where you get

 

[PhanthomJay]

1. A crate is pushed horizontally with a force.
The acceleration of gravity is 9.8 m/s2 .
Calculate the acceleration of the crate.
Answer in units of m/s2

force=1930 N
mass=408 Kg
friction acting on crate=0.26



2. f=ma
u=fk/fn



3. what is the difference between fk and u(friction)? I don't know where to start! :(

When an object is moving. the kinetic friction coefficient, u_k, is the coefficient to use. It is given as u_k =0.26. The kinetic friction coefficient is a property of the 2 materials in contact with each other (might be a wood crate on a concrete pavement, for example. if it was a wood crate being pushed on a soft rubbery surface, u_k might be a higher value.

The term f_k is the force of friction, calculated using your formula, f_k = u_k(fn). Note that u_k is a dimensionless number with no units. It is determined experimentally.

 

[lolkbye]

so my equation would look like
f_k = 0.26((408)(a)) ?

Except I'm trying to find acceleration

 

[PhanthomJay]

so my equation would look like
f_k = 0.26((408)(a)) ?

Except I'm trying to find acceleration

Firstly, look at your equation for f_k, the friction force. You noted that f_k = u_k(f_n). What is the value of f_n, the normal force? It has force units of Newtons. It is calculated by using Newton's first law in the vertical direction. The weight of the crate acts down, so the normal force acts up , and must be equal to the weight, since there is no acceleration in the vertical direction.

Once you solve for f_n, then you can find f_k.

Now that you know f_k, apply Newton's 2nd law in the horizontal direction, F_net = ma, where F_net, the unbalanced force in the horizontal direction, is the algebraic sum of the 2 horizontal forces.