วันอังคารที่ 8 เมษายน พ.ศ. 2557

Calculus applied


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# h3macasp1
A force of 40 N. is required to hold a spring that has been stretched from its
natural length of 10 cm to a length of 15 cm.    How much work is done in stretching
the spring from 15 cm to 18 cm?





Strategy - the rule "Must have" of Mr.Zhang ®
Find the value of k ;f(x)=kx  → (1)
And later find work done (w) from ;  

 → (2)

Solution
Find k(constant of spring) from equation(1)
40 = 0.05k
k =
40
0.05
= 800

Thus, f(x)=800x
And the work done in stretching the spring from 15 cm to 18 cm is
Find work done(w) from equation(2)
w =

=

= 400[(0.18)2-(0.15)2]
= 3.96 J

Ans.    3.96 J work is used for stretching the spring from 15 cm to 18 cm.

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