anonymous 4 years ago hi , i am having a lot of trouble with this problem any help would be appreciated A little cat, Bella, walks in a straight line, which we shall call the x axis, with the positive direction to the right. As an observant scientist, you make measurements of her motion and construct a graph of the little feline's velocity as a function of time. Find the x component of Bella's velocity at t = 4.00 s. give me a sec have to draw graph...

1. anonymous

to see the graph i found the question online here it is http://www.cobaltss.net/forums/lounge-42/anyone-good-physics-151699/

2. anonymous

$v(t)=\frac{-4}{3}t+8$

3. anonymous

$a(t)=\frac{-4}3{}$

4. anonymous

a) t=4 v(t)=-16/3+8 v(t=4)=2.66

5. anonymous

6. anonymous

i mean how did you figure out the first equation you wrote

7. anonymous

ok, the line is passing (0,8) and (6,0) right

8. anonymous

yah

9. anonymous

and we know its slope is -8/6

10. anonymous

yah

11. anonymous

y=mx+n its formula

12. anonymous

okay

13. anonymous

put m=-8/6 and (0,8) or (6,0) to find n

14. anonymous

y=-8/6x+8=-4/3+8

15. anonymous

y=V(t) x=t

16. anonymous

so this is how find the velocity

17. anonymous

|dw:1328511634338:dw|

18. anonymous

and now you have v(t) so you can find v at any time

19. anonymous

yah

20. anonymous

do you know derivative

21. anonymous

kinda of

22. anonymous

this cat is negative accelating (deceleration ) and t=6 v=0 it means at t=6 it stops in a short time and going to opposite side(speed up)..

23. anonymous

dx/dt=v(t) dv/dt=a(t)

24. anonymous

that`s how I found a(t)

25. anonymous

ehats a(t)

26. anonymous

ehats?

27. anonymous

i means whats a(t)

28. anonymous

acceleration at t = 6.00 s.

29. anonymous

you need it for question c,d,e

30. anonymous

what is the difference between velocity and acceleration

31. anonymous

In physics, acceleration is the rate of change of velocity with time

32. anonymous

acceleration is always constant or zero

33. anonymous

if velocity is constant then a is zero

34. anonymous

in your question, v is not constant, it changes with time, so there is an accelation

35. anonymous

|dw:1328512464896:dw|

36. anonymous

|dw:1328512506539:dw|

37. anonymous

so if velocity is constant acceleration is zero if not it changes

38. anonymous

was i suppose to use this equation for this problem

39. anonymous

so if velocity is constant acceleration is zero that's right

40. anonymous

can u take a look at the formula i attached

41. anonymous

you can use it. you know that a is constant and it is -4/3 already v0=8 v(x) we looking for at t=?

42. anonymous

sryy how do you know acceleration constant

43. anonymous

because a is slope of v, v is a line, slope doesnot change in time, it is constant

44. anonymous

as I said before a is zero or constant ALWAYS

45. anonymous

|dw:1328513106159:dw|

46. anonymous

how do you know if it is zero or constant

47. anonymous

take a look graph which I drew at up..

48. anonymous

its constant

49. anonymous

ok, there is always two stuation,

50. anonymous

|dw:1328513296298:dw|

51. anonymous

this one is first stuation..

52. anonymous

the velocity is increasing then decreasing

53. anonymous

velocity is not constant

54. anonymous

yah

55. anonymous

|dw:1328513379149:dw|

56. anonymous

this is secend stuation, v is constant

57. anonymous

yah

58. anonymous

59. anonymous

yah . the last graph you drew show that velocity is zero

60. anonymous

but I drew speed up, yours is speed down

61. anonymous

yah i can see that

62. anonymous

and it has inital velocity which is 8

63. anonymous

so everything is clear now

64. anonymous

so you said acceler is alway zero or constant is velocity is constant its zero. what if velocity is zero

65. anonymous

it means that car remains stop, no act no acce..

66. anonymous

and if acceleration is zero what does that tell you about your car

67. anonymous

if you are driving a car 50 mile/h all the way then your accel is 0 if you are speeding 50 to 100 in 1 min then there is accele. which is const..

68. anonymous

69. anonymous

i apologize for making you repeat but if you have constant velocity , then the acceleration of your car would be...

70. anonymous
71. anonymous

0

72. anonymous

|dw:1328514179090:dw|

73. anonymous

constant velocity

74. anonymous

v doesnt change with time, so a is zero

75. anonymous

so the car is stopped?

76. anonymous

because acceleration is zero

77. anonymous

no, acceleration is zero doesnot require v is zero, v can be zero or constant, either way a is zero

78. anonymous

okay got it thank you

79. anonymous

can you give me some help with the next part

80. anonymous

I need it see it, I cant promise..

81. anonymous

so if i need to find x component of her acceleration at t = 4.00 s.

82. anonymous

i know that her acceleration is constant

83. anonymous

yes, her a is always -4/3 constant you see a(t)=-4/3 doesnot depent on t

84. anonymous

so whatever you plug into t, it will always will be -4/3

85. anonymous

yes.. but for accel right

86. anonymous

i mean whatever you plug in for t into the equation: y=-4/3t+8

87. anonymous

y=-4/3t+8 this eq. is for finding v at some certain time v(t)=-4/3t+8 a and b you need to use this eq. a(t)=-4/3 c,d,e use this formula

88. anonymous

i dont know what to do

89. anonymous

a) t=4 v=(-4/3)*4+8=2.66 is that right

90. anonymous

yah

91. anonymous

or v=v0+at v=8-(4/3)*4

92. anonymous

solve the same way t=7

93. anonymous

ill be back in ahour my battey is low

94. anonymous

ok..

95. anonymous

maybe I can't stay that long..