Lost my formula sheet

1. Dec 15, 2005

DaFuZzMaStA

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

2. Dec 15, 2005

lightgrav

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

You sure this is REVIEW?

3. Dec 15, 2005

andrewchang

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

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

$$\Sigma F = ma$$

4. Dec 15, 2005

DaFuZzMaStA

doesn't help dude haha

5. Dec 15, 2005

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?

6. Dec 15, 2005

Wishbone

hmmmm...recognize this?

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

7. Dec 15, 2005

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!

8. Dec 15, 2005

DaFuZzMaStA

ok that helps..
f=ma right?
so the answer is 40?
k i gotta 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?

9. Dec 15, 2005

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.

10. Dec 15, 2005

Wishbone

what have you done so far?

11. Dec 15, 2005

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

12. Dec 15, 2005

DaFuZzMaStA

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

Last edited: Dec 15, 2005
13. Dec 15, 2005

andrewchang

980 - 784 = 196 ...

14. Dec 15, 2005

DaFuZzMaStA

scale measures 980 newtons

15. Dec 15, 2005

DaFuZzMaStA

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

16. Dec 15, 2005

andrewchang

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

17. Dec 15, 2005

lightgrav

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

18. Dec 15, 2005

andrewchang

yeah, i would agree with that one..

19. Dec 15, 2005

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?

20. Dec 15, 2005

andrewchang

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

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