Question

A 40-m-long chain hangs vertically from a cylinder attached to a winch. Assume there is no friction in the system and the chain has a density of 10 kg/m. Use 9.8 m/s2 for the acceleration due to gravity.
a) How much work is required to wind the entire chain onto the cylinder using the winch?
b) How much work is requeired to wind the chain onto the cylinder if a 25-kg block is attached to the end of the chain??
a) The amount of work required is ____??? J. (Type an integer or a decimal)
b) The amount of work required is ____??? J. (Type an integer or a decimal)

Answer 1

Answer:

a) W₁ = 78400 [J]

b)Wt = 82320 [J]  

Step-by-step explanation:

a) W = ∫ f*dl      general expression for work

If we have a chain with density of 10 Kg/m, distributed weight would be

9.8 m/s² * 10 kg   = mg

Total length of th chain is 40 m, and the function of y at any time is

f(y) = (40 - y ) mg   where ( 40 - y ) is te length of chain to be winded

At the beggining we have to wind 40 meters   y = 0 at the end of the proccess  y = 40 and there is nothing to wind then:

f(y) = mg* (40 - y )

W₁ =  ∫f(y) * dy    ⇒ W₁ = ∫₀⁴⁰ mg* (40 - y ) dy  ⇒ W₁ = mg [ ∫₀⁴⁰ 40dy - ∫₀⁴⁰ ydy

W₁ = mg [ 40*y |₀⁴⁰   -  1/2 * y²  |₀⁴⁰    ⇒  W₁ = mg* [ 40*40 - 1/2 (40)² ]

W₁ = mg * [1/2]     W₁ = 10*9,8* ( 800 )

W₁ = 78400 [J]

b) Now we can calculate work to do if we have a 25 block and the chain is weightless

W₂ = ∫ mg* dy     ⇒    W₂  = ∫₀⁴⁰ mg*dy   ⇒    W₂  = mg y |₀⁴⁰

W₂ = mg* 40   = 10*9.8* 40  

W₂ = 3920 [J]

Total work

Wt = W₁  +  W₂        ⇒    Wt = 78400 + 3920

Wt = 82320 [J]