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 =
.