- #1

BuBbLeS01

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I don't have anything yet because I don't know where to start or what equation to use.

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- Thread starter BuBbLeS01
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- #1

BuBbLeS01

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I don't have anything yet because I don't know where to start or what equation to use.

- #2

kaisxuans

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(visit my blog!)

- #3

Doc Al

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Identify the forces acting on the mass (draw a diagram with forces labeled) and apply Newton's 2nd law.I don't have anything yet because I don't know where to start or what equation to use.

- #4

arildno

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First choose whether "upwards" should be the positive direction or negative.

Then, according to this choice, determine the sign of the known force(s) and accelerations.

The correct sign for the unknown force will then appear out of thin air when you have formulated the problem correctly.

- #5

BuBbLeS01

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I am using f=ma and a I am putting as positive is that not right?

- #6

arildno

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Now, f is the sum of forces acting upon your mass.

What individual forces is f the sum of?

- #7

Doc Al

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Nothing wrong with that, using up = +. What forces act on the mass?I am using f=ma and a I am putting as positive is that not right?

- #8

BuBbLeS01

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the tension and gravityNothing wrong with that, using up = +. What forces act on the mass?

- #9

Doc Al

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Good. Which way do they act? What's the force of gravity equal to? Call the tension "T" and add them up.the tension and gravity

- #10

BuBbLeS01

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gravity acts down (g=9.8) and T acts up.Good. Which way do they act? What's the force of gravity equal to? Call the tension "T" and add them up.

- #11

arildno

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So, weight is a "minus" force, agreed?

Set up Newton's second law!

Set up Newton's second law!

- #12

Doc Al

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Good. Set up an equation per Newton's 2nd law and solve for T.gravity acts down (g=9.8) and T acts up.

- #13

BuBbLeS01

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Fnet=maGood. Set up an equation per Newton's 2nd law and solve for T.

T-g=ma

T=(ma)+g

is that right?

- #14

Doc Al

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Almost.Fnet=ma

T-g=ma

T=(ma)+g

is that right?

- #15

BuBbLeS01

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Okay so its weight that is the force acting down? So T=(ma) + w...I am sorry this question is simple and I am just not getting it and I am so frustrated right now.Almost.is thegaccelerationdue to gravity, but weight is m.g

- #16

Doc Al

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You've almost got it. Keep going!Okay so its weight that is the force acting down? So T=(ma) + w...I am sorry this question is simple and I am just not getting it and I am so frustrated right now.

- #17

BuBbLeS01

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I am getting an answer of 29.4151 N...You've almost got it. Keep going!

- #18

Doc Al

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Sounds about right. Round off your answer to a reasonable number of significant figures.I am getting an answer of 29.4151 N...

- #19

BuBbLeS01

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A sphere of mass of 1.39 kg is accelerated upwards by a string to which the sphere is attached. Its speed increases from 3.01 m/s to 4.81 m/s in a time of 2.28 s. Calculate the tension in the string, assuming that the tension remains constant during that time.

How do you incorporate the speed?

- #20

BuBbLeS01

- 602

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Would you use Vf = Vo + at to find the acceleration?

- #21

BuBbLeS01

- 602

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Oh nevermind I got it!

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