Physics unit 2
What is the net force acting on an object in equilibrium
0
When an object reaches terminal velocity its acceleration is
0
A book weighs 4 N. When held at rest in your hands, the net force on the book is
0 n
A 2000 kg tow truck is pulling a 1000 kg car with a force of 6000 n by how much will the acceleration of the tow truck increase if it let the car loose while maintaining the same forward force
1
Forces of 10 N and 15 N act in oppsite Directions on an object , What is the Net force ?
5
Which exerts more pressure on a shelf a book that is sitting upright or the same book sitting flat on its back cover
A book that is sitting upright
Which produces more pressure on the ground a person standing on their feet or the same person lying on their back
A person standing on their feet
As a care package falls from a high-flying stationary helicopter, its velocity increases and its acceleration
Decreases
Forces always occur in
Pairs
What's pressure measured in
Pascals
A heavy person and a light person parachute together and wear the same size parachutes. Assuming they open their parachutes at the same time, which person reaches the ground first?
The heavy person
An object weighs 30 N on Earth. A second object weighs 30 N on the moon. Which has the greater mass?
The one on the moon
As a ball falls, the action force is the pull of Earth's mass on the ball. What is the reaction to this force?
The pull of the ball's mass on Earth
A person is attracted towards the center of Earth by a gravitational force. The force with which Earth is attracted toward the person is
The same
An unfortunate bug splatters against the windshield of a moving car. Compared to the force of the car on the bug, the force of the bug on the car is ________.
The same
How do the air resistance and the weight of a falling object compare when terminal speed is reached?
They are equal
The law of inertia applies to
both moving and nonmoving objects
An apple weighs 1 N. The net force on the apple when it is in free fall is
1 n
If the pulling force p is 150 n and the crate doesn't move what is the magnitude of f
150 n
A 15 N force and a 45 N force act on an object in opposite directions. What is the net force on the object?
30 N
How does acceleration of an object change in relation to its mass? It is
inversely proportional
Force
is a push or pull
How much mass is contained inside a 100 N dumbell
10.2
How much air resistance acts on a 100 N bag of nails that falls at its terminal speed?
100
Punching through a glass window requires a pressure of 2300 pa if a fist has an area of 0.005 how much force is required to punch through a window
11.5
A 20 N falling object encounters 4 N of air resistance. The magnitude of the net force on the object is
16
A space rocket is carrying a cargo 300 kg of food 550 kg of fuel 150 kg of medical supplies and 250 kg of laboratory supplies if the rocket can take off with a force of 20000 n what acceleration will it experience during launch
16
How much does a 2 kg Apple weigh
19.6 N
If a 300N person goes in a diet and weighs 280 N afterward by how much does this persons mass change
2
If the pulling force p is 200 n and the crate doesn't move what is the magnitude of f
200 n
A tow truck exerts a force of 2000 N on a car, accelerating it at 1 m/s/s. What is the mass of the car?
2000
How much force does a 20,000 kg rocket develop to accelerate 1
20000
A karate chop delivers a blow of 2300 N to a board that breaks. The force that acts on the hand during this feat is ________.
2300
Suppose the force of friction on a sliding object is 25 N. The force needed to maintain a constant velocity is
25
A girl whose weight is 500 N hangs from the middle of a bar supported by two vertical strands of rope. What is the tension in each strand?
250 N
If the force of the sliding friction is 250 n what force is necessary to keep the crate sliding at constant velocity
250 n
If you pull horizontally on a desk with a force of 150 n and the desk doesn't move the friction force must be 150 n now if you pull with 250 n so the desk slides at constant velocity the friction force is 250 n
250 n
When a woman stands with two feet on a scale, the scale reads 280 N. When she lifts one foot, the scale reads
280 n
How much does a 3.5 kg textbook weigh
34.3
A 5 N force and a 30 N force act in the same direction on an object. What is the net force on the object?
35 N
You pull horizontally on a 50 kg crate with a force of 450 N and the friction force on the crate is 250 N. The acceleration of the crate is
4
Two people pull on a rope in a tug-of-war. Each pulls with 400 N of force. What is the tension in the rope?
400
A cheetah must accelerate at a rate of 4 if it hoped to catch its prey as it runs away if the legs of a cheetah can exert a force of 200 n what is the biggest mass that a cheetah can possess if it still hopes to be an effective hunter
50
A sports car has a mass of 1500 kg and accelerates at 5 meters per second squared. What is the magnitude of the force acting on the sports car?
7500
How much force is needed to accelerate a 4 kg physics book to an acceleration of 2
8
Acceleration is equal to force per mass
A =f/m
If action equals reaction, why isn't Earth pulled into orbit around a communications satellite?
According to Newton's third law, Earth pulls on an orbiting communications satellite with the same force the satellite pulls on Earth. Compared to the Earth, the satellite is not very massive so this force will cause it to move noticeably. Compared to the satellite, Earth is massive, so this force will be too small for the movement to be noticeable.
Why do a coin and a feather in a vacuum tube fall with the same acceleration?
All objects have the same weight to mass ratio and fall at the same rate when there is no air resistance
When a high jumper leaves the ground, what is the source of the upward force that accelerates her? What force acts after her feet are no longer in contact with the ground?
As a high jumper jumps, their legs exert a downward force on the ground. The reaction force to this is and upward force on the jumper , pushing the jumper into the air. Once they are in the air, this force continues and eventually gravity will bring them back down to the ground.
If you drop a coin while in a bus that is not moving the coin will land at your feet where will it land if the bus is moving in a straight line at a constant speed
At your feet
Why did Newton think that a force must be acting on the moon?
Because it doesn't move in a straight line
If the moon falls, why doesn't it get closer to Earth?
Because the moon is fast enough to fall around the earth
Bronco the skydiver falls toward Earth. The attraction of Earth on Bronco pulls him down. The reaction to this force is ________.
Bronco pulling up on Earth
How does the tension in your arms compare when you let yourself dangle motionless by both arms and by one arm?
Dangling by one arm doubles the tension
Is force directly or inversely proportional to pressure
Directly
The force of gravity is twice as great on a 2 kg rock as on a 1 kg rock the 2 kg rock falls with twice the acceleration because twice the force acts on twice the mass
False
If the force of gravity suddenly stopped acting on the planets, they would
Fly away from the sun in a straight line
Pressure is defined as
Force per area
What's the formula to calculate pressure
Force/area= pressure (f/a=p)
Accelerations are produced by
Forces
What's true about friction
Friction acts in a direction that opposes the motion of an object
What's true about friction
Friction comes from microscopic bumps that act as obstructions to the objects motion
What's a false statement about friction
Friction is more commonly experienced with smooth surfaces rather than rough ones
What's true about friction
Friction is the name given to the force acting between surfaces sliding past one another
An object following a straight-line path at constant speed
Has no forces acting on it
Why was Copernicus reluctant to publish his ideas?
He feared persecution.
A clothesline is under tension when you hang from it. Is the tension greater horizontal or vertically
Horizontally
inversely proportional
Increasing one variable decreases the other by the same factor
directly proportional
Increasing one variable increases the other by the same factor
Is area inversely or directly proportional to pressure
Inversely
If the force acting on a cart doubles, what happens to the cart's acceleration?
It doubles
Suppose a cart is being moved by a force. If suddenly a load is dumped into the cart so that the cart's mass doubles, what happens to the cart's acceleration?
It halves
What is the effect of friction on a moving object
It slows its motion
Suppose a cart is being moved by a certain net force. If the net force is doubled how does the carts acceleration change?
It will double
A rock is thrown vertically into the air. At the very top of its trajectory the net force on it is
It's weight
Natural rising or falling
Natural motion
Which had more mass a kilogram of iron or feathers
Neither.
What's force measured in
Newton's
Sam decides to apply his physics knowledge to track racing he greases the soles of his running shoes will this strategy work
No
The speed of a ball increases as it rolls down an incline and decreases as it rolls up an incline. What happens to its speed on a smooth, horizontal surface?
No change
If you were in a spaceship and threw a ball into empty space how much force would the ball need to experience to keep it moving at the same speed
No force would be needed
When you jump up, the world really does recoil downward. Why can't this motion of the world be noticed?
Since the mass of the world is very large so the acceleration observed is very small
Fast moving vehicles such as race cars experience greater amounts of air resistance because of the high speeds that they reach which of the following is a common design feature to reduce friction against the air
Surface contour
What is the cause of friction when surfaces slide past one another
Surface irregularities
An arrow is fired from a bow if the action force is the bowstring acting on the arrow identify the reaction force
The arrow acting on the bowstring
A player hits a ball with a bat. The action force is the impact of the bat against the ball. What is the reaction to this force?
The force of the ball against the bat
A player catches a ball. Consider the action force to be the impact of the ball against the player's glove. What is the reaction to this force?
The force the glove exerts on the ball
Galileo found that a ball rolling down one inclined plane would roll how far up another inclined plane?
The same height assuming no friction
A large truck and a small car traveling at the same speed have a head-on collision. The vehicle to undergo the greater change in velocity will be ________.
The small car
The law of inertia states that every object continues in the state of rest or motion unless it is changed by a force. Why then must you continue pedaling your bicycle if you don't want to roll to a stop.
To counter the friction force that slows the bike
Motion imposed on an object
Violent
When swimming you push the water backward...
Water pushes you forward
Why can you go faster on a bicycle if you pull up on the handlebars?
When your body pulls up on the handlebars, the reaction force is The handlebars pushing down on your body . This combines with the downward force of your feet on the pedals resulting in greater total force than if you would not have pulled on the handlebars.
A push on a 1 kg brick accelerates the brick. Neglecting friction, to equally accelerate a 10 kg brick, one would have to push
With 10 times as much force
After a cannonball is fired into frictionless space, the amount of force needed to keep it going equals
Zero
Suppose a cart is being moved by a certain net force. If a load is dumped into the cart so its mass is doubled, by how much does the acceleration change?
it halves
Friction is a force that always acts
opposite to an object's motion
What is meant by the net force that acts on an object
sum of all forces on an object
Pressure
the amount of force exerted per unit area of a surface
A tennis ball and a solid steel ball with the same diameter are dropped at the same time in the absence of air resistance which ball has the greater acceleration
they both have the same acceleration