## milliex51 3 years ago How do I calculate the acceleration of the cart shown, given the following assumption: A frictional resistance of magnitude 2.0 N is acting on the cart.

1. milliex51

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2. henkjan

F = m*a F = 2 N m = 6 kg??? (not really clear what the cart exactly is from your drawing) F = m*a a = F/m a = 2/6 = 1/3 m/s2 (a deceleration, maybe you want to add a minus sign in the force of the resistance)

3. milliex51

The answer is 2.9 m/s ^2 [fwd] in the back of my book.. but

4. henkjan

than i misinterpretted your picture, let me guess again :P

5. milliex51

and I found the formula for no friction only: T = m1a a = m2g/(m1 + m2)

6. hyunaelee

F=MA. Which means summation of forces is equal to mass times acceleration. There are two different blocks so there are two different free body diagrams. Block of 4 KG. There's a force normal and a force gravity and a force friction and a force tension. Block of 2 KG. There's a force tension and a force gravity only. So for the 2nd block Ft-Fg= MA. --> Ft-2.0(9.8)=2.0(a) ---> 4.0a+2.0-2.0(9.8)=2.0a solve for a 1st block. Ft-Ff=MA. ---> Ft-2.0 = 4.0(a) Ft=4.0a+2.0

7. TuringTest

m=4kg from her pic

8. milliex51

ohhh.. I think I'm getting it. o.o

9. milliex51

May I ask why ft - Fg = ma?

10. milliex51

sometimes I don't get these formulas >_<"

11. hyunaelee

Look at the block. Look at what's "touching it" And then there are also 4-non contact forces that can act upon the block. Force gravity, electric force, magnetism force, and I forget the last one

12. milliex51

yes, tension force? normal force? applied force?

13. hyunaelee

So for the 2.0 KG block only a rope is touching the block. Which is Force Tension (Ft) and a non-contact force force gravity (Fg)

14. cwrw238

equtoion of motion for 2.5kg is 2.5g - T = 2.5a ......................................4kg is T - 2 = 4.5a solving this sytem will give you the reqd acceleration

15. TuringTest

because total force=ma and the total force is force of the object pulling on one end of the string minus the friction force (because it is acting in the opposite direction).

16. milliex51

yup, I see it! :)

17. milliex51

ohhhhhhhh.

18. milliex51

thank you!!

19. hyunaelee

No problem. I hope you understand the problem now ^_^. Remember to draw free body diagrams of the entire system and remember contact forces and non-contact forces

20. milliex51

yeah I will! Wait, what do you mean by contact and non-contact forces? Like tension force, gravity force, normal force, applied force... etc?

21. TuringTest

gravity force is non-contact because it touches nothing in order to impart a force on it.

22. hyunaelee

Contact is forces that are literally touching the object you are drawing the free body diagram for. Non contact forces are "invisible" forces. There are only 4 forces that are "invisible" but I think the only one you'll ever face in basic physics is "Force Gravity". There are two more for more advanced physics "Electrical and Magnetism". Contact forces can be : Force friction (From a surface) or force tension (from a rope) force spring (from a spring) and much more

23. milliex51

ohhhh, i see, i see. THANK YOU S O MUCH!! :D

24. cwrw238

you sure its 2.9 m/s/s for acceleration

25. hyunaelee

No problems. Good luck ^_^ and hope you do well.