## micahwood50 3 years ago A 2-kg body rests on frictionless wedge that has an inclination of 60º and an acceleration a to the right such that the mass remains stationary relative to the wedge. Find a.

1. micahwood50

|dw:1349586481376:dw|

2. Algebraic!

3. micahwood50

No, we didn't.

4. micahwood50

Still don't understand the force...

5. micahwood50

FBD: |dw:1349586646724:dw| Not sure if it's right, though.

6. Algebraic!

|dw:1349586759042:dw|

7. severus

acos60=gcos30 (Balancing forces along the wedge in the reference frame of the wedge)

8. Algebraic!

heh

9. Algebraic!

|dw:1349587034552:dw|

10. Algebraic!

a= gtan60

11. micahwood50

How do you set the equation for y? Not sure if I'm doing it right...\[\Sigma F_y = Nsin60º = ma\]

12. Algebraic!

Ncos60 - mg =0

13. micahwood50

Hold on, give me time.

14. micahwood50

Why Ncos60, not sin?

15. Algebraic!

look at the sketch

16. Algebraic!

Nsin30 - mg =0 (if you like)

17. micahwood50

Yeah, silly me. Got it. Just give me a little more time.

18. micahwood50

Can you explain me why Nsin60º = ma?

19. Algebraic!

because there are only two forces acting on the mass... N and mg. if you think about it, it's magic otherwise... because if the block is being accelerated it can only be because the ramp is 'pushing' it... ie the Normal force...

20. Algebraic!

if the block were somehow accelerated otherwise, it would be some magical force:)

21. micahwood50

Now you're making it a little clear. If the wedge was given a greater cceleration, the block will slip upward, right?

22. micahwood50

acceleration*

23. Algebraic!

it's like sitting in a car seat when someone stomps on the gas... you feel pushed back but the actuality is that the seat's Normal force has increased and is acting to accelerate you...

24. Algebraic!

No.:)

25. micahwood50

Why not?

26. Algebraic!

N would get longer, but it would still be perp. to the ramp face...

27. Algebraic!

you're thinking maybe of a more "real-life" situation wherein air resistance is a factor... then yes, the block would slide up the ramp at some point...

28. micahwood50

Now you're mention about air resistance, it does make block slide up. Thanks.

29. Algebraic!

hmm actually, maybe you're right about that...

30. Algebraic!

because mg is fixed so... if N stays perp. to the ramp face and ma gets longer...I guess N would have a y component larger than mg....

31. micahwood50

Hmm I see. It does make sense.

32. Algebraic!

I answered too quickly... sorry :P

33. micahwood50

It's ok. You helped me a lot. Thanks. I wish I could give you more medals, lol.

34. Algebraic!

heh.