1. YumYum247

A 60 Kg person gets on an elevaator in the Mclennan Physics labs at the university of Toronto. Naturally, there's a scale (measuring Newtons) on the floor, The person steps on the scale and presses "UP". The scale reads 700N (UP). Determine the acceleration of the elevator. Draw a free body diagram.

2. YumYum247

|dw:1442526744201:dw|

3. YumYum247

The natural force pushing down o nthe person is = Fn = 60Kg (9.80m/sec^2) = 588N(Down)

4. YumYum247

5. YumYum247

Fn = 588(down) Fs = 700N (UP) Fs = m.a - m.g Fs = |dw:1442527123799:dw|

6. YumYum247

7. YumYum247

am i even remotely close to the right track?

8. Astrophysics

:3

9. YumYum247

:D

10. YumYum247

true.

11. Astrophysics

|dw:1442528711236:dw| here's the thing, when the elevator is going up, the acceleration of elevator = acceleration of student

12. Astrophysics

$F_{net}=T+W$ so these are the only forces acting on the student

13. YumYum247

his weight and what...T?

14. Astrophysics

Tension (scale)

15. YumYum247

ok is the tension given to us or nah? no right.

16. Astrophysics

It is, 700N :)

17. YumYum247

ok....:D

18. Astrophysics

As the student is rising the scale reads 700N

19. YumYum247

so his acceleration is 700N X 60kg?

20. Astrophysics

$ma = T+mg \implies a = \frac{ T+mg }{ m }$

21. YumYum247

|dw:1442528962628:dw|

22. Astrophysics

The 60 kg is mass not weight, weight is a force

23. Astrophysics

W = mg

24. YumYum247

OMG I'm Sorry :(

25. Astrophysics

xD

26. YumYum247

27. Astrophysics

Tension is the applied force here, which be exerted by pushing or pulling the object, but since the elevator is going up, it is being pulled so that is the applied force here (Tension) which is opposing weight

28. YumYum247

Oh ok cuz i know it by F sub applied, i didn't know it's tension too..

29. Astrophysics

Applied force = tension, it doesn't matter :P, people often confuse it

30. Astrophysics

Different notations with same meanings pretty much

31. YumYum247

ok Thanks...just one last thing....could you please name the follow...

32. YumYum247

m.a = ? M.g = ? T = Fapplied

33. Astrophysics

What do you mean?

34. YumYum247

does net force = m.a right?

35. Astrophysics

Weight = mg Newton's second law = ma, in the case it's the net force

36. Astrophysics

F=ma*

37. Astrophysics

Yes

38. YumYum247

I got it.... Thanks and I LOVE YOU SHOOOOOO MUCH!!!! <3

39. Astrophysics

By the way, there is a trick question with elevators you may run into

40. YumYum247

41. Astrophysics

If you ever have a question that says, the elevator is moving up/down what ever at a CONSTANT VELOCITY that implies acceleration = 0

42. YumYum247

OOOOOOOOOooooooooooooooooooooooooooo!!!! Thanks.....:")

43. Astrophysics

Yw :) teachers often like to trick students with stuff life that, you have to remember your kinetmatics during those questions

44. YumYum247

i've mastered my kinematics!!!

45. YumYum247

:D

46. YumYum247

Anyways plz don't go, i may need your help....thanks :")

47. Astrophysics

:)

48. YumYum247

OH btw Weight = Normal Force right??????????

49. Astrophysics

Well...if there is a surface, and then the perpendicular force would be same as weight.

50. YumYum247

ok i'll take that as a yes!!!!!

51. Astrophysics

|dw:1442529792131:dw|

52. Astrophysics

But for the elevator, there is no normal force when it's moving

53. YumYum247

ok thanks :")

54. YumYum247

|dw:1442530093066:dw|

55. YumYum247

does it look ok ?????

56. Astrophysics

Note the direction of the forces

57. YumYum247

the 60kg will cancel out right?????

58. YumYum247

ok sorry!! :)

59. Astrophysics

$\vec F _{net}= \vec T + \vec W \implies m \vec a = \vec T +m \vec g \implies \vec a = \frac{ \vec T +m \vec g }{ m }$

60. Astrophysics

g = - 9.81 m/s^2

61. YumYum247

oh really?????

62. YumYum247

g = -9.81....ok thanks....but 60kg will cancel out right??????

63. Astrophysics

Why?

64. Astrophysics

It can be $\vec a = \frac{ \vec T }{ m }+ \vec g$

65. YumYum247

because kg.m/sec^2 = N if i'll have 2N in the numerator and kg in the denominator...

66. YumYum247

ok that still doesn't make things easier to solve :(

67. YumYum247

|dw:1442530594548:dw|

68. YumYum247

|dw:1442530658933:dw|

69. YumYum247

|dw:1442530740704:dw|

70. YumYum247

|dw:1442530801983:dw|

71. YumYum247

i got it!!! :"D

72. YumYum247

@Astrophysics I Love you dear!!!! :") :D

73. YumYum247

Thanks a mol.

74. Astrophysics

:)