Elastomer-Evaluate the work of extension to l. PLEASE HELP BOOK ANSWER WRONG ?

i really dont know how they got this answer in the book, please help thank yo

NCS2018-04-22T15:08:39Z

Favorite Answer

No, the answer isn't wrong. It's basic integration.
w = ∫ F(x) dx = ∫ k(x)*x dx = ∫ (a - bx^½)*x dx = ∫ (ax - bx^(3/2)) dx = ½ax² - (2/5)bx^(5/2) + C
which when evaluated between 0 and ℓ yields
w = ½aℓ² - (2/5)bℓ^(5/2)

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