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Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: missbeautiful789 on October 24, 2010, 09:49:34 am

Title: Springs and momentum. 1 question CIE M/j 06 5(c)
Post by: missbeautiful789 on October 24, 2010, 09:49:34 am

<a href="http://tinypic.com?ref=2qtl1lk" target="_blank"><img src="http://i52.tinypic.com/2qtl1lk.jpg" border="0" alt="Image and video hosting by TinyPic">[/url]
(http://i52.tinypic.com/2qtl1lk.jpg)

M/j 06 5(c)
Please could someone help me with this question, im not sure which approach to use. Much appreciated  ;D

Title: Re: Springs and momentum. 1 question CIE M/j 06 5(c)
Post by: Deadly_king on October 24, 2010, 10:25:09 am

I take it that you found the solution to part (b)

Work done by spring = 1/2 k ( x₂² -  x₁²)

c) You should find out the gain in strain energy of spring using the equation above. But you need to convert k in Nm^-1 first. Hence k = 1600Nm^-1

Gain in energy strain energy for both springs = 1/2(1600)(0.06² - 0.045²) + 1/2(1600)(0.03² - 0.045²) = 0.36 J

Strain energy gets converted into kinetic energy of trolley.
K.E = 1/2mv² = 0.36

Taking m as 0.85kg ----> V = 0.92 ms^-1

Hope it helps :)

Title: Re: Springs and momentum. 1 question CIE M/j 06 5(c)
Post by: missbeautiful789 on October 24, 2010, 11:43:14 am

I used the formula from b.
my problem is:
I found that the work don to the right is 1.26J
And the work done to the left is -0.9J
so shouldn't the total work done on the mass be 1.26-(-0.9) to the right
so instead of 0.36, why isn't it 2.16J

(http://i52.tinypic.com/8y5g5u.jpg)

Title: Re: Springs and momentum. 1 question CIE M/j 06 5(c)
Post by: Deadly_king on October 24, 2010, 12:44:25 pm

Quote from: missbeautiful789 on October 24, 2010, 11:43:14 am

I used the formula from b.
my problem is:
I found that the work don to the right is 1.26J
And the work done to the left is -0.9J
so shouldn't the total work done on the mass be 1.26-(-0.9) to the right
so instead of 0.36, why isn't it 2.16J

(http://i52.tinypic.com/8y5g5u.jpg)

Hehe.........my dear missbeautiful789

Energy is a scalar quantity. So it cannot be negative ;)

Title: Re: Springs and momentum. 1 question CIE M/j 06 5(c)
Post by: missbeautiful789 on October 24, 2010, 01:29:41 pm

Doh.. :o
thats what you get for blindly following formulas

+Rep DK

Title: Re: Springs and momentum. 1 question CIE M/j 06 5(c)
Post by: Deadly_king on October 24, 2010, 02:18:17 pm

Quote from: missbeautiful789 on October 24, 2010, 01:29:41 pm

Doh.. :o
thats what you get for blindly following formulas

+Rep DK

Hahahaha..........guess you are right :D

You should be glad you made the mistake here and not in exams ;)