7.63 Set Up:
For part (a) use
to solve for
W
, the energy the bulb uses. Then set this value equal to
for
part (b), and solve for the speed. In part (c), equate the
W
from part (a) to
and solve for the height.
Solve: (a)
(b)
so
(c)
so
Reflect: (b)
Olympic runners achieve speeds up to approximately
or roughly one third the result calculated.
(c)
The tallest tree on record, a Redwood, stands 364 ft or 110 m, or 4.7 times smaller than the result.
7.64. Set Up:
Use the relation
to relate the given power and velocity to the force required. Recall that a
watt represents the rate of energy—a joule per second.
Solve:
The force required is thus
7.65. Set Up:
Since the electricity cost rate is given in cents per
each power must be multiplied by the
corresponding time usage in determining the cost:
Solve: (a)
(b)
Reflect:
Note that the cost of running the motor for an entire day is
thus, the cost of running the
motor is
times the cost of running the light.
7.66. Set Up:
This is the end of the preview. Sign up
to
access the rest of the document.
This note was uploaded on 03/06/2009 for the course PHYS 114 taught by Professor Shoberg during the Spring '07 term at Pittsburg State Uiversity.
 Spring '07
 Shoberg
 Energy

Click to edit the document details