Problems 227
Problem 8.35
8.29. The drum of a clothing dryer is turning at a rate of 1
revolution every second when you suddenly open the
door of the dryer. You noticed that it took 1.5 seconds
for the drum to completely stop. Determine the decel-
eration of the drum. State your assumptions.
8.30. A drill bit is turning at a rate of 1200 revolutions per
minute when you suddenly stop it by turning off the
power. If the deceleration of the bite is 40 rad /s
2
, how
long would it take for the bit to completely stop?
8.31. On a gusty windy day, the blades of a wind turbine are
turning at a rate of 200 revolutions per minute when
suddenly the brakes are applied to stop the turbine to
avoid failure. If the brakes cause a deceleration of 2
rad /s
2
, how long would it take for the blades of the
wind turbine to come to rest?
8.32. A plugged dishwasher sink with the dimensions of 2 ft
1.5 ft1 ft is being filled with water from a faucet
with an inner diameter of 1 in. If it takes 35 seconds to
fill the sink to its rim, estimate the volumetric flow of
water coming out of the faucet. What is the average
velocity of water coming out of the faucet?
8.33. Imagine the plug in the sink described in Problem 8.32
leaks. If it now takes 40 seconds to fill the sink to its
rim, estimate the volumetric flow rate of the leak.
8.34. A rectangular duct with dimensions of 12 in14 in
delivers conditioned air to a room at a rate of 1000
ft
3
/min. What should be the size of a circular duct if
the average air velocity inside the duct is to remain the
same?
8.35. The tank shown in the accompanying figure is being
filled by Pipes 1 and 2. If the water level is to remain
constant, what is the volumetric flow rate of water leav-
ing the tank at 3? What is the average velocity of the
water leaving the tank?Pipe 1:
d 1 = 1 in.
V 1 = 2 ft/s1 Pipe 2:
d 2 = 1.75 in.
V 2 = 1.5 ft/sPipe 3:
d 3 = 1.5 in.
V 3 =?238.36. Imagine that the water level in Problem 8.35 rises at a
rate of 0.1 in /s. Knowing the diameter of the tank is
6 in., what is the average velocity of the water leaving
the tank?
8.37. If it takes a bicyclist 20 seconds to reach a speed of
10 mph from rest, what is her acceleration? For the
next 10 minutes, she moves at the constant speed of
10 mph, and at this time, she applies her brakes, and
the bicycle decelerates to a full stop in 4 seconds. What
is the total distance travelled by the bicyclist? Deter-
mine the average speed of the cyclist during the first
20 seconds, 620 seconds, and 624 seconds.
8.38. An object is dropped from the roof of a high-rise build-
ing at a distance of 450 ft. Prepare a table similar to
Table 8.3 showing the speed and acceleration of the
object and the distance travelled by the object as a func-
tion of time.
8.39. Solve Problem 8.38 for a situation in which the object
is given an initial vertical upward velocity of 4 ft /s.
Again, prepare a table similar to Table 8.3 showing the
speed and acceleration of the object and the distance
travelled by the object as a function of time.
8.40. Determine the natural frequency of the system given
in Example 8.1 if its mass is doubled.
8.41. The period of oscillation for a pendulum on Earth is
2 seconds. If the given pendulum oscillates with a period
of 4.9 seconds on the surface of the Moon, what is the
acceleration due to gravity on the Moon’s surface? Express
your answer in both SI and U.S. Customary units.
8.42. What is the period of oscillation of the pendulum given
in Problem 8.40 on Mar’s surface? Given gEarth9.81
m/s
2
and gMars3.70 m/s
2
.
8.43. The power to an electric motor running at a constant
speed of 1600 rpm is suddenly turned off. It takes
10 seconds for the motor to come to rest. What is the
deceleration of the motor? How many turns does the
motor make before it stops. State your assumptions.
8.44. The 2009 World Record for the 100-m sprint is 9.58
seconds and belongs to a Jamaican runner named
Usain Bolt. Assuming constant acceleration, determine
the speed of Mr. Bolt at distances of 10 m, 20 m, 30 m,... , 80 m, 90 m, and 100 m.
8.45. The 1994 men’s pole vault World Record of 6.14 m
belongs to Mr. Sergey Bubka of Ukraine. If the pole vault
mat has the dimensions of 6.0 m8.0 m0.8 m,
what is the vertical speed of the vaulter (Mr. Bubka) right
before he strikes the mat?
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