10. Physics Applications of Integrals

A $40m$ rope hangs freely over a ledge. The density of the rope is $12\mathrm{kg}$/$m$. If a $5\mathrm{kg}$ bucket is attached to the end of the rope, how much work is done to pull the rope and the bucket to the ledge?

A $60\mathrm{ft}$ cable is attached to a cylinder that is attached to a winch. If the cable weighs 300 lbs, how much work is needed to wind $20\mathrm{ft}$ of the cable onto the cylinder using the winch? Hint: Divide cable weight by cable length to get density.

A water trough for horses has a triangular cross section with a height of $3m$ and horizontal side lengths of $2m$. The length of the trough is $12m$. How much work is required to pump the water to the top of the trough when it is half full.

A swimming pool has the shape of a rectangular prism with abase that measures 30 $\mathrm{ft}$ by 20 $\mathrm{ft}$ and is 5 $\mathrm{ft}$ deep. The top of the pool is 1 $\mathrm{ft}$ above the surface of the water. How much work is required to pump all the water out? Assume the density of water is 62.4 $\mathrm{lb}$/$f{t}^3$.

90. Work Let R be the region in the first quadrant bounded by the curve y = √(x⁴ - 4)

and the lines y = 0 and y = 2. Suppose a tank that is full of water has the shape of a solid of revolution obtained by revolving region R about the y-axis. How much work is required to pump all the water to the top of the tank? Assume x and y are in meters.

Explain how to find the mass of a one-dimensional object with a variable density ρ.

Why is integration used to find the work required to pump water out of a tank?

9–12. Consider the cylindrical tank in Example 4 that has a height of 10 m and a radius of 5 m. Recall that if the tank is full of water, then ∫₀¹⁰ 25 π ρg(15−y) dy equals the work required to pump all the water out of the tank, through an outflow pipe that is 15 m above the bottom of the tank. Revise this work integral for the following scenarios. (Do not evaluate the integrals.)

The work required to empty the top half of the tank

9–12. Consider the cylindrical tank in Example 4 that has a height of 10 m and a radius of 5 m. Recall that if the tank is full of water, then ∫₀¹⁰ 25 π ρg(15−y) dy equals the work required to pump all the water out of the tank, through an outflow pipe that is 15 m above the bottom of the tank. Revise this work integral for the following scenarios. (Do not evaluate the integrals.)

The work required to empty the tank through an outflow pipe at the top of the tank

Emptying a cylindrical tank A cylindrical water tank has height 8 m and radius 2m (see figure).

a. If the tank is full of water, how much work is required to pump the water to the level of the top of the tank and out of the tank?

Emptying a cylindrical tank A cylindrical water tank has height 8 m and radius 2m (see figure).

b. Is it true that it takes half as much work to pump the water out of the tank when it is half full as when it is full? Explain.

Work from force How much work is required to move an object from x=0 to x=3 (measured in meters) in the presence of a force (in N) given by F(x)=2x acting along the x-axis?

Work from force How much work is required to move an object from x=1 to x=3 (measured in meters) in the presence of a force (in N) given by F(x) = 2x² acting along the x-axis?

Compressing and stretching a spring Suppose a force of 30 N is required to stretch and hold a spring 0.2 m from its equilibrium position.

c. How much work is required to stretch the spring 0.3 m from its equilibrium position?

Compressing and stretching a spring Suppose a force of 30 N is required to stretch and hold a spring 0.2 m from its equilibrium position.

d. How much additional work is required to stretch the spring 0.2m if it has already been stretched 0.2m from its equilibrium position?