What is the formula for calculating friction and normal force in physics?

[DaFuZzMaStA]

And doign some old review I'm going to need some really simple help. (Hah, grade 11 physics )
200 N accelerates a 20kg sled at 8.0m/s^2
It's asking the force of friction..
Just give me a formula please :)

 

[lightgrav]

Sum of Force vectors causes the center-of-mass to accelerate.

You sure this is REVIEW?

 

[andrewchang]

... perhaps you should find another site with equations? if you search online, you can find one.

http://www.physicsgre.com/physics-equations.shtml

$$\Sigma F = ma$$

 

[DaFuZzMaStA]

doesn't help dude haha

 

[andrewchang]

this definitely doesn't seem like "review".

if you apply a 200 N force to the sled, then how much should it accelerate? how much does it actually accelerate? so then what is the force of the friction?

 

[Wishbone]

hmmmm...recognize this?

F(net) = F(friction) + F(applied)

 

[lightgrav]

Your turn, to show what you're thinking.
If you've ever taken physics of ANY kind before,
you have to know how to add Force vectors!

 

[DaFuZzMaStA]

ok that helps..
f=ma right?
so the answer is 40?
k i got to harder one :S
an 80kg guy is on a scale on an elevator and it shows his wait is 980..
how fast is the elevator going?

 

[andrewchang]

do you know how to draw a free body diagram?

what forces are acting on him? what force is measured by a scale?
and the question should ask how fast is the elevator accelerating.

 

[Wishbone]

what have you done so far?

 

[DaFuZzMaStA]

yeah it does.. force of gravity is 784 (m times a)
force of gravity is acting on him.. and the force of the elevator which is going up? it does ask how fast the elevator is accelerating..
i drew free body diagram
and i got fnet = f - fg

 

[DaFuZzMaStA]

so ma = 980 - 784
80a=196
a = 2.5 m/s^2 ?

 

[andrewchang]

980 - 784 = 196 ...

 

[DaFuZzMaStA]

scale measures 980 Newtons

 

[DaFuZzMaStA]

wow
must of typed that into the calculator wrong ><
so my answer is 2.5?

 

[andrewchang]

yes he accelerates at 2.5 m/s^2. upwards. acceleration is a vector.

 

[lightgrav]

2.45 m/s^2 (upward) ... units are perhaps more important than the numbers.

 

[andrewchang]

yeah, i would agree with that one..

 

[DaFuZzMaStA]

ok a block has a 60n force pulling at 30 degrees above the horizontal
i did the sin and cos and that
the Fn should be 30n and the force to the right? (not sure what to call that) is 52 N
How do i find acceleration from here?

 

[andrewchang]

how did you know the normal force without knowing the weight..?

 

[Tide]

Since you're just looking for formulas here's a couple of them - just for you:

$$A = \pi r^2$$

$$\rho = \frac {M}{V}$$

$$a^2 + b^2 = c^2$$

$$x = \frac {-b + \sqrt{b^2 - 4ac}}{2a}$$

I hope that helps! :)

 

[DaFuZzMaStA]

umm
well i just found the force that was pulling up on it
isn't that the normal force?

 

[andrewchang]

haha, tide

i think i can give some too:

$$sin( \Theta) = \frac {opposite}{hypotenuse}$$
$$\Delta x = vt$$
$$ln( \frac {VP_1}{VP_2}) = \frac {\Delta H}{R}(\frac {1}{T_2} - \frac {1}{T_1})$$

 

[andrewchang]

and no, that wouldn't be the normal force. The normal force would be the weight - the force of the pull in the y direction. but you don't have the weight? as long as it's frictionless, you should be fine.

 

[DaFuZzMaStA]

no weight and its frictionless..
but the question before the one I am doing now has the same thing and asks to calculate the normal force..
dont worry about it
i'm goin to school early tomorrow to get someone to help (y)
peace out