# Ch 9.3 Help

## Ch 9.3 Help

**Question 1**A compressed spring with a spring constant of 129.4 N/m has 8.015 J potential energy stored in it. How far is the spring compressed from its relaxed state (see sheet 22)? Indicate with a positive (negative) sign whether the spring has a different (the same) potential energy stored in it when it is stretched by the same amount.

__How To Solve__

Answer is

**Question 2**A spring with a spring constant of 53.899 N/m which is aligned vertically is compressed by 18.426 cm from its relaxed state. A 0.1338 kg mass is then placed on the spring and the spring is released. What is the kinetic energy of the mass as it lifts off from the relaxed spring (see sheet 24)? Indicate with a negative (positive) sign whether the mass gains and the spring looses potential energy (or the other way around).

__How To Solve__

Answer is

**Question 3**A 0.5295 kg block attached to a spring with a spring constant of 52.3 N/m oscillates frictionless with an amplitude of 0.2722 m on a horizontal plane. What is the maximum velocity of the block (see sheet 27)? Indicate with a negative (positive) sign whether one can calculate from the data given the total energy of the mass-spring system for any given time during the oscillation (or not).

__How To Solve__

Answer is

**Question 4**A pendulum with a string length of 52.47 cm swings back and forth. You push it whenever it has come to rest at a turning point. With which frequency do you have to push it in order to cause resonance, that is maximal energy build up in the oscillation (see sheet 29,33,34)? Indicate with a negative (positive) sign whether your result depends (does not depend) on the mass suspended from the string.

__How To Solve__

Answer is

*[Note: Currently working on it]*

**Guest01**- Posts : 133

Join date : 2008-09-19

## ch 9.3 Questions

Could someone please help with these I have been working on them for a while and I am having a lot of trouble?

**hwilson**- Guest

## Re: Ch 9.3 Help

Easy there guys, it's not due until another 4 days.

What do you not exactly get? What does your work look like?

What do you not exactly get? What does your work look like?

**Guest01**- Posts : 133

Join date : 2008-09-19

## Re: Ch 9.3 Help

Are you guys even trying... some of this is right off of the lecture slides directly. If you're actually having trouble, post up your work and I'll correct it but I mean... c'mon.

**gwar**- Guest

## quiz questions

I have number 1 and number 3? Can anyone help with 4 I am still working on number 2?

**guest22**- Guest

## Answers

1. negative

2. negative

3. negative

4. positive

1. Formula: [(2*PE)/K]^.5 = X

2. Formula: V^2= sqrt[(.5kx^2-mgx)/.5m]

Then KE= .5mv^2

3. Formula: Vo^2= [K*(x_0^2)]/m

Then, take the sqrt

4.Formula: T= 2pi*sqrt(L/g)

Then divide 1 by T to get f. So if T=2, f= 1/2= .5

Don't forget to change to meters. Hope this helps, good luck.

2. negative

3. negative

4. positive

1. Formula: [(2*PE)/K]^.5 = X

2. Formula: V^2= sqrt[(.5kx^2-mgx)/.5m]

Then KE= .5mv^2

3. Formula: Vo^2= [K*(x_0^2)]/m

Then, take the sqrt

4.Formula: T= 2pi*sqrt(L/g)

Then divide 1 by T to get f. So if T=2, f= 1/2= .5

Don't forget to change to meters. Hope this helps, good luck.

**helpme**- Guest

## question 2

for the formula of question 2 there shouldn't be a sqrt since you're looking for v^2

**101**- Guest

## Question 2

Can someone pleease help me?? I keep getting #2 wrong...

Here's what I did...

A spring with a spring constant of 56.039 N/m which is aligned vertically is compressed by 15.416 cm from its relaxed state. A 0.0894 kg mass is then placed on the spring and the spring is released. What is the kinetic energy of the mass as it lifts off from the relaxed spring (see sheet 24)?

V^2=sqrt([(.5*56.039*.15416^2)-(.0894*9.81*.15415)]/(.5*.0894))

V^2=sqrt((.6659-.1352)/.0447

V^2=3.446

KE=(.5*.0894*3.446)

KE=.15402 (-)

I must of did this problem like 4 times!! What am I doing wrong??

Here's what I did...

A spring with a spring constant of 56.039 N/m which is aligned vertically is compressed by 15.416 cm from its relaxed state. A 0.0894 kg mass is then placed on the spring and the spring is released. What is the kinetic energy of the mass as it lifts off from the relaxed spring (see sheet 24)?

V^2=sqrt([(.5*56.039*.15416^2)-(.0894*9.81*.15415)]/(.5*.0894))

V^2=sqrt((.6659-.1352)/.0447

V^2=3.446

KE=(.5*.0894*3.446)

KE=.15402 (-)

I must of did this problem like 4 times!! What am I doing wrong??

**Meg**- Guest

## Re: Ch 9.3 Help

Does anyone know pro. Dawber's email address I looked under staff info and I didnt see anything there.... Thanx

**Guest 87**- Guest

## Re: Ch 9.3 Help

Question 2

KE= 1/2kx^2-mgx

straight off the lecture notes. the method posted above does not work

KE= 1/2kx^2-mgx

straight off the lecture notes. the method posted above does not work

**1**- Guest

## Re: Ch 9.3 Help

The first formula for Question 2 worked for me. Just remember if you find the square root then in the KE formula you have to square the

**v**again. You can also just leave it as is and do*.5*m*v*(not squared).**Guest01**- Posts : 133

Join date : 2008-09-19

## Question 1

Alright, first list all the given quantities

Now what is the question, what are you looking for?

Think of an appropritate equation/formula that would satisfy the problem.

Well,

Okay, so now solve for the unknown, the

So:

Then:

Therefore: sqrt [

**PE**= some# (check!)**k**= some# (check!)Now what is the question, what are you looking for?

__How far has the spring compressed?__(In other words, the distance**)**__x__**x**= ? <------- unknown, which also happens to be the answerThink of an appropritate equation/formula that would satisfy the problem.

Well,

**PE**= 1/2***k*****x**^2 pops into mind, don't you agree?Okay, so now solve for the unknown, the

**x**So:

**PE**= 1/2***k*****x**^2Then:

**PE**/ (.5***k**) =**x**^2Therefore: sqrt [

**PE**/ (.5***k**) ] =**x****Shrubbs**- Posts : 3

Join date : 2008-10-31

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