Physics Newton's 3 Laws
Terms in this set (38)
Suppose a cart is being moved by a certain net force. If the net force is doubled, by how much does the cart's acceleration change?
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?
Cuts in half
If the force of friction acting on a sliding crate is 100 N, how much force must be applied to maintain a constant velocity? What will be the net force acting on the crate? What will be the acceleration?
100 N in opposite direction
Fnet = 0
a = 0
Distinguish between force and pressure
Force = Push Pull
Which produces more pressure on the ground, a person standing up or the same person lying down?
A person standing- less area in contact with ground
The force of gravity is twice as great on a 2-kilogram rock as on a 1-kilogram rock. Why does the 2-kilogram rock not fall with twice the acceleration
a = Net/m = weight/m = mg/m = g for all objects
Why does a feather and a hammer fall with the same acceleration on the moon?
No air resistance to slow the feather
How much air resistance acts on a 100-N bag of nails that falls at its terminal speed?
Terminal velocity = air resistance balances weight
How do the air resistance and the weight of a falling object compare when terminal speed is reached?
They are equal
All other things being equal, why does a heavy sky diver have a greater terminal speed than a light skydiver? What can be done so that both terminal speeds are equal?
Take longer for air resistance to balance weight of heavy sky diver
Heavy diver- Decrease surface area
Light diver- Increase surface area
In the interaction between a hammer and the nail it hits, is a force exerted on the nail? On the hammer? How many forces occur in this interaction?
When a hammer exerts a force on a nail how does the amount of force compare with that of the nail on the hammer?
When you walk along the floor, the action force is: you push the floor. What is the reaction force?
Floor pushes you
When swimming, the action force is: you push the water backward. What is the reaction force?
Water pushes you forward.
If the action force is: a bowstring pushes an arrow forward. What is the reaction force?
Arrow pushes bowstring backward
When you jump up, the world really does recoil downward. Why can't this motion of the world be noticed?
Mass of world is much greater than you mass
When a rifle is fired, how does the size of the force of the rifle on the bullet compare with the force of the bullet on the rifle? How does the acceleration of the rifle compare with that of the bullet? Why?
Rifle has much more mass
How can a rocket be propelled above the atmosphere where there is no air to "push against"?
As long as rocket has fuel to shoot out if rocket pushes fuel, fuel pushes rocket
If you hit a wall with a force of 200 N, how much force is exerted on you?
Why can't you hit a feather in midair with a force of 200 N?
Because the feather can't hit you back with 200 N
If the the action force is the earth pulls on you, what is the reaction force?
You pull on the earth
What is the net force action on a 25-N object in free fall? What is the net force when the object encounters 15 N of air resistance? What is the net force when the object falls fast enough to encounter 25 N of air resistance?
When blocking in football, why does a defending lineman often attempt to get his body under that of his opponent and push upward (think about what effect this has on the friction force between the opposing lineman's feet and the ground)?
Decreases friction force making it easier to push player around
In terms of pressure, why does a sharp knife cut better than a dull knife?
Sharp knife has less area which creates more pressure
Why is it safe for a person to sit on a bed of nails but unsafe to sit on a single nail?
More nails = more area = less pressure
An aircraft gains speed during takeoff due to the constant thrust of its engines. When is the acceleration during takeoff greatest- at the beginning of the run along the runway or just before the aircraft lifts into the air? Think about air resistance, then explain.
Greatest acceleration at the beginning because when the place is just starting there is not much resistance
An aircraft gains speed during takeoff due to the constant thrust of its engines. When is the speed during take off greatest-- at the beginning of the run along the runway or just before the aircraft lifts into the air?
Even though air resistance decreases acceleration, speed is increasing throughout runway trip- greatest speed just before takeoff
As a skydiver falls faster and faster through the air (before reaching terminal speed), does the net force on there increase, decrease, or stay the same? Does her acceleration increase, decrease of stay the same?
Net force decreases because of air resistance
Acceleration decreases because net force decreases
After she jumps, a skydiver reaches terminal speed after 10 seconds. Does she gain more speed during the first second of fall or the ninth second of fall? (Think about net force.) Compared with the first second of fall, does she fall a greater or a lesser distance during the ninth second?
The first second of fall
Greater during ninth second
If you walk on a go that is floating in the water, the log moves backward. Why?
If the log pushes me forward, I push log backward.
If you step off a ledge, you accelerate noticeable toward the earth because of the gravitational interaction between you and the earth. Does the earth accelerate toward you as well?
Suppose you're weighing yourself while standing next to the bathroom sink. Using the ida of action and reaction, explain why the scale reading will be less when you push down on the top of the sink. Why will the scale reading be more if you pull on the bottom of the sink?
If I push down on the sink, sink pushes up on me- resealing in lower scale reading
If I pull up on sink, sink pushes down on me- resulting in greater scale reading
If the action force is : the earth pulls on a communications satellite with a force of 1000 N. What is the reaction force? If the action equals reaction, why isn't the earth pulled into orbit around the communication satellite?
Communication satellite pulls earth with 1000 N force
Mass of earth is much greater than mass of satellite
If a bicycle and a massive truck have a head-on collision, upon which vehicle is the impact force greater? Which vehicle undergoes the greater change in its motion?
Neither, it's equal
Bicycle because it has less mass
A speeding bus makes contact with a bug that splatters onto the windshield. Because of the sudden force, the unfortunate bug undergoes a sudden deceleration. Is the corresponding force that the bug exerts against the windshield greater, less, or the same? Is the resulting deceleration of the bus greater than, less than, or the same as that of the bug?
Much less because bus mass is much greater than bug mass
Some people used to think that a rocket could not travel to the moon because it would have no air to push against once it left the earth's atmosphere. We now know that idea was mistaken. What force propels a rocket when it is in a vacuum?
Rocket pushes fuel so fuel pushes rocket
Since the force that acts on a bullet when a gun is fired is equal and opposite to the force that acts on the gun, does this imply a zero net force and therefore the impossibility of an accelerating bullet? Explain.
Not the forces act on different objects. Each object has only one force on it- they don't cancel
Suppose you exert 200 N on your refrigerator and push it across the kitchen floor at a constant velocity. What friction force acts between the refrigerator and the floor? Is the friction force equal and opposite to your 200-N push? Does the friction force make up the action to your push?
200 N in opposite direction
Yes the friction force is equal and opposite
No it has nothing to do with the friction
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