- #1

- 3

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Okay I know the formula for a spring is F=-kx

So k=mg/x

converting the cm to m I get 4.18cm = 0.0418m

So I plug in my numbers

k=(9.09kg)(9.81m/s^2)/ 0.0418

but that gives me 2133 which is not the answer.

What am I doing wrong?

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- Thread starter Crbeach
- Start date

- #1

- 3

- 0

Okay I know the formula for a spring is F=-kx

So k=mg/x

converting the cm to m I get 4.18cm = 0.0418m

So I plug in my numbers

k=(9.09kg)(9.81m/s^2)/ 0.0418

but that gives me 2133 which is not the answer.

What am I doing wrong?

- #2

- 22

- 1

(9,09 * 9,81) / (4,18^(-2)) = 1 558,06458

If that is the right answer than you just made a typo, if it's not then I also don't know:P

- #3

ehild

Homework Helper

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Include the unit of the spring constant.

ehild

ehild

- #4

- 3

- 0

The answer is 2.13 kg*m/s^2 / m

The only way I can see to get that answer is to make the cm into decimeters

4.18 cm = 41.8 dec

That gives me 2.13 but that wouldn't work for the unit kg*m/s^2 /**m**

The only way I can see to get that answer is to make the cm into decimeters

4.18 cm = 41.8 dec

That gives me 2.13 but that wouldn't work for the unit kg*m/s^2 /

Last edited:

- #5

ehild

Homework Helper

- 15,543

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Your answer k=2133 N/m is correct if the mass is 9.09 kg. If the mass is 9.09 g (gram) k would be 2.13 N/m.

ehild

- #6

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Thank you very much. Its nice to know I was doing the problem correctly

- #7

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The problem assumes that the spring starts from the relaxed length with zero force. The force at the maximum compression is the peak force (mg). Since k is a constant, the relationship between force and distance is linear. So, the average force is 1/2 of the peak force (1/2 * m * g).

- #8

ehild

Homework Helper

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I'm guessing that you were off by a factor of 2. In the Hooke's Law equation (F = -kx) where force is generated by gravity, F represents the AVERAGE force, not the peak force.

That is wrong.

F=-kx is the force the spring exerts on the block when its length differs by x from the relaxed length, not an "average" one. The block is stationary, so the force of gravity is cancelled by the spring force, mg-kx=0.

ehild

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