EK physics lecture 3 question 321

[howyoudoin]

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can some one show me the math. I set MGH= 1/2kxsqrd I can not get this answer

 

[Rabolisk]

What's the question?

 

[howyoudoin]

A 2kg Block is dropped from a 45cm above a spring. If the spring compresses 5cm when struck by the block what is the spring constant?

 

[shffl]

Did you remember to convert cm to m?

MGH = 1/2kx^2

k = 2mgh/x^2
k = 2(2)(10)(0.5)/(0.05^2)
k = 20/0.0025
k = 8000

 

[TwoPaddles]

What you have to realize is 1) conversion of units and, 2) addition of 5 cm to the 45 cm to get the total height (because it is dropped from 45 cm height and it's compressing 5 cm more ...meaning the total height is 50 cm)

 

[ilovemcat]

What you have to realize is 1) conversion of units and, 2) addition of 5 cm to the 45 cm to get the total height (because it is dropped from 45 cm height and it's compressing 5 cm more ...meaning the total height is 50 cm)

Yep. I missed this problem because of #2, hah.