[ Pobierz całość w formacie PDF ]
initial total energy of the system,
pulled to the right, such that the
frictional force, and (e) the
(b) the work done against friction as
rope makes an angle of 30.00 with
coefficient of friction.
m slides on the rough surface,
2
the vertical, what is (a) the
(c) the velocity v of mass m as it
1 1
maximum potential energy of the
hits the ground, and (d) the kinetic
girl, (b) her maximum kinetic
energy of m as it hits the ground.
1
energy, and (c) the maximum
velocity of the swing and where
does it occur?
7.7 Further Analysis of the
Conservation of Energy
31. A 3.56-kg mass moving at a
speed of 3.25 m/s enters a region Diagram for problem 33.
Diagram for problem 38.
where the coefficient of kinetic
friction is 0.500. How far will the 34. A 1.00-kg block is pushed
*39. A 5.00-kg body is placed at
block move before it comes to rest? along a rough horizontal floor with
the top of the track, position A, 2.00
32. A 5.00-kg mass is placed at a horizontal force of 5.00 N for a
m above the base of the track, as
the top of a 35.00 rough inclined distance of 5.00 m. If the block is
shown in the diagram. (a) Find the
plane that is 30.0 cm high. The moving at a constant velocity of
total energy of the block. (b) The
coefficient of kinetic friction 4.00 m/s, find (a) the work done on
block is allowed to slide from rest
between the mass and the plane is the block by the force, (b) the
down the frictionless track to the
0.400. Find (a) the potential energy kinetic energy of the block, and
position B. Find the velocity of the
at the top of the plane, (b) the work (c) the energy lost to friction.
body at B. (c) The block then moves
done against friction as it slides
over the level rough surface of µ =
k
down the plane, (c) the kinetic 35. A 2200-N box is pushed
0.300. How far will the block move
energy of the mass at the bottom of along a rough floor by a horizontal
before coming to rest?
the plane, and (d) the velocity of the force. The block moves at constant
mass at the bottom of the plane. velocity for a distance of 4.50 m. If
the coefficient of friction between
the box and the floor is 0.30, how
much work is done in moving the
box?
36. A 44.5-N package slides
from rest down a portion of a
circular mail chute that is at the
height h = 6.10 m above the ground.
Diagram for problem 39.
Chapter 7 Energy and Its Conservation 7-25
direction, (d) the total energy at the
40. A 0.500-kg ball is dropped top of the trajectory, (e) the
from a height of 3.00 m. Upon potential energy at the top of the
hitting the ground it rebounds to a trajectory, (f) the maximum height
height of 1.50 m. (a) How much of the projectile, (g) the kinetic
mechanical energy is lost in the energy at the top of the trajectory,
rebound, and what happens to this and (h) the velocity of the projectile
Diagram for problem 48.
energy? (b) What is the velocity just as it hits the ground.
before and just after hitting the 45. It takes 20,000 W to keep a
49. A mass m = 3.50 kg is
ground? 1600-kg car moving at a constant
launched with an initial velocity v
speed of 60.0 km/hr on a level road.
= 1.50 m/s from the position A at a
Additional Problems How much power is required to
height h = 3.80 m above the
*41. The concept of work can be keep the car moving at the same
reference plane in the diagram for
used to describe the action of a speed up a hill inclined at an angle
problem 48. Paths A-B and C-D of
lever. Using the principle of work in of 22.00 with the horizontal?
the track are frictionless, while
equals work out, show that 46. John consumes 5000
path B-C is rough with a coefficient
kcal/day. His metabolic efficiency is
of kinetic friction of 0.300 and a
F = r F 70.0%. If his normal activity utilizes
out in in
length of 3.00 m. Find (a) the
r 2000 kcal/day, how many hours will
out
number of oscillations the block
John have to exercise to work off
makes before coming to rest along
Show how this can be expressed the excess calories by (a) walking,
the path B-C and (b) where the
in terms of a mechanical advantage. which uses 3.80 kcal/hr;
block comes to rest on path B-C.
(b) swimming, which uses 8.00
50. A ball starts from rest at
kcal/hr; and (c) running, which uses
position A at the top of the track.
11.0 kcal/hr?
Find (a) the total energy at A,
47. A 2.50-kg mass is at rest at
(b) the total energy at B, (c) the
the bottom of a 5.00-m-long rough
velocity of the ball at B, and (d) the
inclined plane that makes an angle
velocity of the ball at C.
of 25.00 with the horizontal. When a
constant force is applied up the
plane and parallel to it, it causes
the mass to arrive at the top of the
Diagram for problem 41.
incline at a speed of 0.855 m/s. Find
(a) the total energy of the mass
*42. Show how the inclined
when it is at the top of the incline,
plane can be considered as a simple
(b) the work done against friction,
machine by comparing the work
and (c) the magnitude of the applied Diagram for problem 50.
done in sliding an object up the
force. The coefficient of friction
plane with the work done in lifting
between the mass and the plane is 51. A 20.0-kg mass is at rest on
the block to the top of the plane.
0.350. a rough horizontal surface. It is
How does the inclined plane supply
*48. A 2.00-kg block is placed at then accelerated by a net constant
a mechanical advantage?
the position A on the track that is force of 8.6 N. After the mass has
43. A force acting on a 300-g
3.00 m above the ground. Paths A-B moved 1.5 m from rest, the force is
mass causes it to move at a
and C-D of the track are removed and the mass comes to rest
constant speed over a rough
in 2.00 m. Using energy methods
frictionless, while section B-C is
surface. The coefficient of kinetic
find the coefficient of kinetic
[ Pobierz całość w formacie PDF ]