860 Solutions Manual
Problem 5.11
Consider an elevator that moves with an operating speed of
2:5 m=s
. Suppose that a person who boards the elevator on the
ground floor gets off on the fifth floor. Assuming that the elevator
has achieved operating speed by the time it reaches the second
floor and that it is still moving at its operating speed as it passes
the fourth floor, determine the momentum change of a person with
a mass of
80 kg
between the second and fourth floors if each floor
is
4
m high. In addition, determine the impulse of the person’s
weight during the same time interval.
Solution
of McGraw-Hill, and must be surrendered upon request of McGraw-Hill. Any duplication or distribution, either in print or electronic form, without the
permission of McGraw-Hill, is prohibited.
Dynamics 2e 861
Problem 5.12
A
180 gr
(
7000 gr D1lb
) bullet goes from rest to
3300 ft=s
in
0:0011
s. Deter-
mine the magnitude of the impulse imparted to the bullet during the given time
interval. In addition, determine the magnitude of the average force acting on
the bullet.
Solution
of McGraw-Hill, and must be surrendered upon request of McGraw-Hill. Any duplication or distribution, either in print or electronic form, without the
permission of McGraw-Hill, is prohibited.
862 Solutions Manual
Problem 5.13
A
3400 lb
car is parked as shown. Determine the impulse of the normal reaction force acting on the car
during the span of an hour if ✓D15ı.
Solution
We model the car as a particle subject to its own weight, the propelling
force
F
, and the normal force with the ground
N
. We can determine
N
Dynamics 2e 863
Problem 5.14
A
3850 lb
sports car (driver’s weight included), driving along a horizontal rectilinear stretch of road, goes
from 0to 62 mph in 4:2 s.
Determine the magnitude of the average force that needs to be applied to the car for such an acceleration
to occur.
Solution
864 Solutions Manual
Problem 5.15
A
3850 lb
sports car (driver’s weight included), driving along a horizontal rectilinear stretch of road, goes
from 0to 62 mph in 4:2 s.
If the magnitude of the force propelling the car has the form
F01et=⌧
, with
⌧D0:5
s, determine
F0.
of McGraw-Hill, and must be surrendered upon request of McGraw-Hill. Any duplication or distribution, either in print or electronic form, without the
permission of McGraw-Hill, is prohibited.
Dynamics 2e 865
Problem 5.16
A
75 lb
crate is initially at rest when a force
PD40 lb
is applied to the pulley system
as shown. Use the impulse-momentum principle to determine the speed of the crate
after
2
s. Neglect the inertia of the rope and of the pulleys, and assume that all the
cable segments are purely vertical.
Solution
866 Solutions Manual
Problem 5.17
The pulley system shown is at rest when the motor
M
starts pulling in rope
so as to lift the
120 lb
cargo
C
. For the first second of operation, the motor
can produce a tension in the rope of the form
F0.1 Ct=⌧/
, where
F0D40 lb
.
Neglect the inertia of the pulleys and of the rope.
If
⌧D0:5
s, use the impulse-momentum principle to determine the speed
of the crate after 1s.
Solution
We model the cargo
C
as a particle subject only to its own weight
mg
and three
times the tension in the cord
Fc
. For convenience, we let
t1D0
and
t2D1
s. We
Dynamics 2e 867
Problem 5.18
The pulley system shown is at rest when the motor
M
starts pulling in rope
so as to lift the
120 lb
cargo
C
. For the first second of operation, the motor
can produce a tension in the rope of the form
F0.1 Ct=⌧/
, where
F0D40 lb
.
Neglect the inertia of the pulleys and of the rope.
Use the impulse-momentum principle to find the value of
⌧
needed for the
cargo Cto travel upward with a speed of 10 ft=s after 1s.
Solution
of McGraw-Hill, and must be surrendered upon request of McGraw-Hill. Any duplication or distribution, either in print or electronic form, without the
permission of McGraw-Hill, is prohibited.
868 Solutions Manual
Problem 5.19
A box comes off of a conveyor belt with a speed
v0D3m=s
and then slides
over a low-friction surface. Determine the coefficient of kinetic friction between
the crate and floor if the box slides 1:5 s before coming to a stop.
Solution
We model the box as a particle subject only to its own weight
mg
and the force due
to the contact with the sliding surface, which we have split into the components
N
Dynamics 2e 869
Problem 5.20
A
60-ton
railcar and its cargo, a
27-ton
trailer, are moving to the
right at
4mph
when they come into contact with a bumper that
can bring the system to a stop in
0:78
s. Determine the magnitude
of the average force exerted on the railcar by the bumper.
Solution
of McGraw-Hill, and must be surrendered upon request of McGraw-Hill. Any duplication or distribution, either in print or electronic form, without the
permission of McGraw-Hill, is prohibited.