**Practice 1: **Using geometry (Fig. 17): so .

Using integrals:

The single integral is **not** correct: .

**Practice 2:**

cars per hour.

**Practice 3: **.

**Practice 4: **(a) force = (force for cable) + (force for object)

= (length of cable)(density of cable) + 10 pounds

pounds.

(b) "from the ground to a height of 10 feet:"

(a Riemann sum)

as the mesh approaches 0.

"From a height of 10 feet to a height of 20 feet:" work = .