P199 Homework 1
A 50-N object falling in air experiences 50 N of air resistance. The amount of net force on the falling object is
0 N.
An object travels 8 m in the 1st second of travel, 8 m again during the 2nd second of travel, and 8 m again during the 3rd second. Its acceleration is
0 m/s^2
What is the acceleration of a car that maintains a constant velocity of 100 km/h for 10 s?
0 m/s^2
The vertical height attained by a basketball player who achieves a hang time of a full 1 s is about
1.2 m.
A 1-kg mass at Earth's surface weighs about
10 N.
Place a book that weighs 10 N on a horizontal surface and the support force on the book is
10 N.
The force of friction on a sliding object is 10 N. The applied force needed to maintain a constant velocity is
10 N.
If a freely falling object were somehow equipped with a speedometer, its speed reading would increase each second by about
10 m/s.
The gain in speed each second for a freely falling object is about
10 m/s.
At the end of two seconds of free fall, an object released from rest will have a speed of
10 m/s. 5 m/s. 15 m/s. **none of the above**
When a falling object gains 10 m/s each second, its acceleration is
10 m/s^2.
Fido weighs 120 N and carries Trixie who weighs 40 N on her back. The support force on Fido's feet is
160 N.
You're driving in a car at 50 km/h and bump into a car ahead traveling at 48 km/h in the same direction. The speed of impact is
2 km/h.
A 50-N object falling in air experiences 30 N of air resistance. The amount of net force on the falling object is
20 N.
The average speed of a horse that gallops a distance of 10 km in a time of 30 min is
20 km/h.
If a freely falling object were somehow equipped with a speedometer on a planet where the acceleration due to gravity is 20 m/s2, then its speed reading would increase each second by
20 m/s.
An object is pulled with three forces: one at 20 N to the right, another at 40 N to the right, and the third at 30 N to the left. The net force is
30 N to the left. 60 N to the right. 60 N to the left. **none of the above**
A man weighing 800 N stands at rest on two bathroom scales so that one scale shows a reading of 500 N. The reading on the other scale is
300 N.
A 3000-N bear grasping a vertical tree slides down at constant velocity. The friction force between the tree and the bear is
3000 N.
If a Jaguar sports car accelerates from zero to 100 km/h in 3.0 s its acceleration is
33.3 km/h/s.
The average speed of a deer traveling a distance of 2 km in a time of one-half hour is
4 km/h.
If a ball rolls down an inclined plane and picks up 4 m/s each second it rolls, its acceleration is
4 m/s^2
A man weighing 800 N stands at rest on two bathroom scales so that his weight is distributed evenly over both scales. The reading on each scale is
400 N.
Burl and Paul have a total weight of 1300 N. The tensions in the ropes that support the scaffold they stand on add to 1700 N. The weight of the scaffold itself must be
400 N.
When a 10-kg block is simultaneously pushed toward the east with 20 N and toward the west with 15 N, the combination of these forces on the block is
5 N east.
An object is pulled with two forces, 10 N northward and 15 N southward. The magnitude of the net force is
5 N.
When a 10-N object is suspended at rest by two vertical strands of rope, the tension in each rope is
5 N.
One-half second after starting from rest, a freely falling object will have a speed of about
5 m/s.
Nellie runs the length of a 100-yard football field in a time of 20 seconds. Her average running speed is
5 yards/s
A girl pushes a cart to the left with a 100-N force. A boy pushes it to the right with a 50-N force. The net force exerted on the cart is
50 N to the left.
A free-falling object has a speed of 30 m/s at one instant. Exactly 2 seconds later its speed will be
50 m/s.
An object in free fall has a speed of 60 m/s. One second later its speed is
70 m/s.
Suppose that an object in free fall were somehow equipped with a speedometer. By how much would its speed readings increase with each second of fall?
9.8 m⋅s−1
In a dream you're in a car traveling at 50 km/h and you bump into another car traveling toward you at 48 km/h. The speed of impact is
98 km/h.
A. In the absence of air resistance, a ballplayer tosses a ball straight up. By how much does the speed of the ball decrease each second while it is ascending? B. By how much does its speed increase each second while it is descending? C. How does the time of ascent compare with the time of descent?
A. 9.8 m⋅s−1 B. 9.8 m⋅s−1 C. The time of ascent equals the time of descent.
A horizontal force of 160 N is required to push a bookcase across a floor at a constant velocity. A. What is the net force acting on the bookcase? B. How much is the friction force that acts on the sliding bookcase? C. How much friction acts on the bookcase when it is at rest on a horizontal surface without being pushed?
A. F = 0 N B. Ffr = -160 N C. Ffr = 0 N
Find the net force produced by a 36-N force and a 28-N force in each of these cases. A. Both forces act in the same direction. B. The two forces act in opposite directions.
A. F = 64 N B. F = 8.0 N
A. Find the acceleration for a ball that starts from rest and rolls down a ramp and gains a speed of 24 m/s in 3.8 s . B. Would acceleration be greater or less if the ramp were a bit less steep?
A. a = 6.3 m/s^2 B. Acceleration would be less on a less-steep ramp.
A. Find the average speed of a tennis ball when it travels the full length of the court, 24 m, in 0.60 s . B. How would air resistance affect the travel time?
A. vavg = 40 ms B. Air resistance would increase travel time.
Knowledge can be gained by philosophical logic and also by experimentation. Which of these did Aristotle favor, and which did Galileo favor?
Aristotle favored logic; Galileo favored experiment.
The scientist to first introduce the concept of inertia was
Galileo.
You would have the largest mass of gold if it weighed 1 N on the
Moon.
When you stand at rest on a pair of bathroom scales, the readings on the scales will always
add to equal your weight.
You hang from a pair of gym rings and the upward support forces of the rings will always
add up to equal your weight.
You're lying on the sand on a breezy day when a pesky fly wishes to join you. The breeze is blowing at a steady 2 m/s. In order for the fly to land on you it should hover over you while flying
against the breeze at 2 m/s.
Which has zero acceleration?
an object in mechanical equilibrium an object at rest an object moving at constant velocity
Which has the greatest mass?
automobile battery
If Burl carried Paul piggy-back while standing in the middle of a scaffold, the tensions in the two supporting ropes would
be equal.
Aristotle treated motion by
classifying it into two classes.
When sign painters Burl and Paul stand on opposite ends of a scaffold, the tensions in each of the two supporting ropes
depend on the relative weights of Burl and Paul.
The two measurements necessary for calculating average speed are
distance and time.
A parachutist falling at constant velocity is in a state of
dynamic equilibrium.
In contrast to Aristotle's way of explaining nature, Galileo relied on
experiment
Science greatly advanced when Galileo favored
experiment
According to Galileo, the test of scientific truth is
experiment.
A motor scooter undergoes acceleration when it
gains speed. changes direction. decreases speed.
When a crate slides down an incline at a constant velocity it is
in dynamic equilibrium.
During each second of free fall, the speed of an object
increases by the same amount.
An object that has twice as much mass as another object also has twice as much
inertia
Compared with a 1-kg block of solid iron, a 2-kg block of solid iron has twice as much
inertia. volume. mass.
A glance at your speedometer will tell you your
instantaneous speed.
When a ball increases in speed by the same amount each second, its acceleration
is constant.
Whenever the net force on an object is zero, its acceleration
is zero.
When Galileo rolled a ball down an incline and up another incline, he found that the ball rolled nearly to
its initial height.
Galileo said that if you rolled a ball along a level surface it would
keep rolling without slowing down if no friction acted upon it.
The resistive force of friction occurs for
liquids. gases. solids.
Aristotle believed that natural laws could be understood by
logic
On the surface of the Moon where acceleration due to gravity is less, a person's hang time would be
longer.
A kilogram is a measure of an object's
mass.
What physical quantity is a measure of how much inertia an object has?
mass.
At the end of 2 seconds of free fall, an apple falling from rest has a speed of
more than 10 m/s.
An object in mechanical equilibrium is an object
moving at constant velocity. at rest. with no acceleration.
The equilibrium rule F = 0 applies to
objects or systems in uniform motion in a straight line. objects or systems at rest.
According to Galileo, inertia is a
property of all matter.
Galileo's demonstration at the Leaning Tower of Pisa
refuted Aristotle's teachings.
An object is pulled with two forces, 10 N northward and 15 N southward. The direction of the net force is to the
south
The amount of friction that occurs when two blocks slide against each other depends on
the "stickiness" of atoms on their surfaces. how much they are pressed together.
An object weighs 30 N on Earth. A second object weighs 30 N on the Moon. The object with the greater mass is the one on
the Moon.
Your weight is
the gravitational attraction between you and Earth.
When you push your desk to the right, friction on the desk acts toward
the left.
When you push a crate across a level floor at constant speed, friction between the crate and the floor is
the same amount as your pushing force.
Compared with the mass of a certain object on Earth, the mass of the same object on the Moon is
the same.
Someone standing at the edge of a cliff throws a ball straight up at a certain speed and another ball straight down with the same initial speed. If air resistance is negligible, predict which ball will hit the ground below with greater speed, or whether they will hit at the same speed.
they will hit at the same speed
When she hikes a distance of 1 km in a time of one-half hour her average speed is
twice 1 km/h.
When you stand at rest on a floor, the number of vertical forces acting on you is
two.
Calculate your average walking speed when you step 0.90 m in 0.46 s .
vavg = 2.0 m/s
The speed of a vertically-thrown ball at the top of its path is
zero.
