Physics chapter 5
Each of these boxes is pulled by the same force F to the left. All boxes have the same mass and slide on a friction free surface. Rank the following from the greatest to least. A)The accelerations of the boxes B)The tensions in the ropes connected to the single boxes to the right in B and in C
A) A, B, C B) Cb are equal
For each of the following interactions, identify action and reaction forces; A) a hammer hits a nail B) Earth's gravity pulls down on a book. C) A helicopter blade pushes air downward
A) A-the hammer hits the nail. R-the nail exerts an equal but opposite force on the hammer. B)A-The earth's gravity pulls down on a book, R-the book pulls up on earth. C) A-a helicopter blade pushes air downward, R-the air pushes up on the helicopter with an equal but opposite force.
Why does vertically falling rain make slanted streaks on the side windows of a moving automobile? If the streaks make an angle of 45 degress, what does this tell you about the relative speeds of the car and the falling rain?
A) As the rain moves down the window, the car moves foward making the rain flow go toward the back. B) They are moving at the same rate.
As a tossed ball sails through the air, a force of gravity mg acts on it. Identify the reaction to this force. Also identify the accleration of the ball along its path, even at the top of its path.
Ball is tossed and pulls upward, gravity pulls downward on it. Accerlation=9.8m/s^2 or will remain constant
Within a book on a table, there are billions of forces pushing and pulling on all the molecules. Why is it that these forces never by chance add up to a net force in one direction, causing the book to accelerate "sponteanously" across the table?
Because they are within the same system. There needs to be an external force to make the object move.
Ken and Joanne are astronauts floating some distance apart in space. They are joined by a safety cord whose ends are tied around their waists. If Ken starts pulling on the cord, will he pull Joanne toward him, or will he pull himself toward Joanne, or will both astronauts move? Explain.
Both will move because of Newtons 3rd law and first. Newton's 3rd-When Ken pulls the rope, the rope also pulls on him and moves and Newtons 1st law-Joanne will move because a force is exerted upon her.
When you kick a football, what action and reaction forces are involved? Which force, if either, is greater?
Foot pushes on the football and the football pushes back on the foot. Both are equal but opposite.
Why can you exert a greater force on the pedals of a bicycle if you pull up on the handlebars?
If you pull up on the handlebars, it adds more of a downward force because it is equal but opposite, it produces more power than your legs alone can do giving you a greater force.
Two 100N weights are attached to a spring sclae as shown. Does the scale read 0, 100, or 200 N or does it give some other reading? (Would the reading be different if one of the ropes were tied to the wall instead of to the handing 100 N weight?
It reads 100 and it would be the same if it was tied to the wall it would still be 100 N. The tension within the rope 100N
The strong man can withstand the tension force exerted by the two horses pulling in opposite directions. How would the tension compare if only one horse pulled and the left rope were tied to a tree? How would the tension compare if the two horses pulled in the same direction, with the left rope tied to the tree?
It would be the same. If two horses pull in the same direction, then the tension in the ropes is doubled.
In Figure 5.25 how does the magnitude of f relate to the vector sum of mg and N when the shoe is in equilibrium? What ocurs if f is less than this sum?
N and mg are equal but opposite of f. b) it will roll because f will be less than that sum
You push a heavy car by hand. The car, in turn, pushes back with an opposite but equal force on you. Doesn't this mean that the forces cancel each other, making acceleration impossible? Why or why not?
No, because if you're pushing externally from the car, it can't be canceled since it is external. If it was within the same system, then yes.
When you rub your hands together, can you push harder on one hand than the other?
No, because they both have to push with an equal but opposite force to move.
Here the stone is sliding down a friction free incline, a) Identify the forces that act on it, and draw appropraite force vectors. b)Use the parallelogram rule to construct the resultant force on the stone (carefully showing that it has a direction parallel to the incline-the same direction as the stone's acceleartion)
Normal force, resultant, w acts straight down due to gravity
A stone is suspended at rest by a string. a) Draw force vectors for all the forces that act on the stone. B) Should your vectors have a zero resultant? c) Why or Why not?
R=0. Because the stone is not moving and they are equal.
A baseball bat is swung against a baseball, which accelerates. When the ball is caught, what produces the force on the player's glove?
The baseball accelerates because the bat hitting the ball is the Action force. The force the ball exerts after being on by the bat produces the force on the players glove.
Refer to Monkey Mo in Figure 5.26. What will be teh magnitude of vector S if the rope that supports Mo is vertical? If the rope were horizontal, how would vector S be different? Why can't both vectors T and S be horizontal?
The magnitude of vector S will be 0 if the rope that supports Mo is vertical. He will just be hanging with no forward motion. The same goes for if it was horizontal. T and S can't be both horizontal because they will cancel each other out if they're in the same system
There are two interactions that involve a stone at rest on the ground. One is between the stone (mg) and the stone pulls up on Earth. What is the other interaction.
The surface of the stone and the surface of the Earth. When the stone is pushing down on the surface of the Earth, the surface of the earth is holding it up. The surface of the earth is it's support force.
In a tug-of-war between Sam and Maddy, each pulls on the rope with a force of 250 N. What is the tension in the rope? If both remain motionless, what horizontal force does each exert against the ground?
The tension in the rope is 250 N. Since they are not accelerating, each must experience a 250 N force of friction against the ground. This happens because they're pushing against the ground with a force of 250 N.
Two people of equal mass attempt a tug-of-war with a 12m rope while standing on frictionless ice. When they pull on the rope, each of them slides towards the other. How do their accelerations compare, and how far does each person slide before they meet?
Their accelerations are the same because their masses are the same. Mass and acceleration are irreversely proportional. They will both slide 6 m to meet each other in the middle.
Suppose that two carts, one twice as massive as the other, fly apart when the compressed spring that joins them is released. What is the acceleration of the heavier cart relative to that of the lighter cart as they start to move apart?
They have the same speed, but because they have different masses their acceleration is different. The bigger the mass, the smaller the aceleration. So the 2m-less acceleration and speed while the "m" will have greater speed and acceleration.
When the athlete holds the barbell overhead, the reaction force is the weight of the barbell on his hand. How does this force vary for the case in which the barbell is accelerated upward? Downward?
Upward= you push up on the barbell and it pulls down on you. Downward-You pull down on the barbell and it pushes up, away from you.
What physics is involved for a passenger feeling pushed backward into the seat of an airplane when it accelerates along the runway during take off?
When the airplane accelerates, the seat pushes you forward, then you simultaneously, equally and oppositely push backward against the seat.
Identify the action-reaction pairs of forces for the following situations. a) you step off a curb. b) You pat your tutor on the back. c) a wave hits a rocky shore.
a) A-Step off a curb, R-earth meets your foot-the curb pushes back on your foot. b) A-Pat tutor on the back, R-tutor's back pushes back on your hand. c) A-The wave exerts a force on the rocky shore, R-The rocky shore exerts a force on the waves.
Suppose the string in the preceding exercise breaks and the stone slows in its upward motion. Draw a force vector diagram of the stone when it reaches the top of its path
both vectors are equal because there is no net force on an object at the top of its path
