HOMEWORKQUESTIONS: WEEK 5
For each of the following interactions, identify action and reaction forces: (a) A hammer hits a nail. (b) Earth gravity pulls down on a book. (c) A helicopter blade pushes air downward.
(a) when a hammer hits a nail, it pushes against it (the action). The nail reacts and pushes back on the hammer (the reaction), therefore recoiling the hammer away from the nail. (b) the gravity of the earth pushes on the book (action), then the book reacts and pushes against gravity (reaction). If the book falls, gravity is pushing the book down, while the book is also pushing against gravity, which would result in acceleration. (c)when a helicopter's blades whirl, it is pushing air molecules downwards (action), then the air molecules react by moving upwards, therefore pushing the helicopter further up.
Is gravitational force acting on a person who falls off a cliff? On an astronaut inside an orbiting space shuttle?
Gravitational force is acting on a person who falls off a cliff, and on a n astronaut in a orbiting space shuttle. Both of them are falling under the influence of gravity.
Does the gravitational force between two objects always depend on mass and distance
The strength of the gravitational force between two objects depends on mass and distance. Therefore I assume that mass and distance are always needed.
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 different masses, so their acceleration would be different. The bigger the mass, the smaller the acceleration. So, the "2m" would have less acceleration and speed, while the "m" will have greater speed and acceleration due to the change in mass.
An astronaut lands on a planet that has twice the mass on Earth and twice the diameter. How does the astronaut's weight differ from that on Earth?
To solve this problem, we can look at the law of universal gravitation, which is F=G(m1m2)/r^2. Weight is equal to the force of gravity acting upon us. The force is directly proportional to the product of the masses and inversely proportional to the square of the distance. If you double the mass of the planet, the astronaut's weight will double. However, the diameter of the planet is also twice as large, which decreases the astronaut's weight by a factor of 4. Therefore, the astronaut's weight on the new planet will be 1/2 of what his weight was on Earth. F=G(m1x2m2)/(2r^2)- F=G(m1x2m2)/4r This show's that the astronaut's weight will be halved on the new planet.
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 greatest to least:
a. The acceleration of the boxes. b. The tensions in the ropes connected to the single boxes to the right in B and C. a. A, B, C b. C, B, A
Calculate the force of gravity on the same 1-kg mass if it were 6.4 3 10^6 m above Earth's surface (that is, if it were two Earth radii from Earth's center).
F=G m1 1m2/d2=6.67x10-11 Nxm^2/kg^2 x(1kg)(6x10^24kg)/[2(6.4x10^6m)]^2=2.5N
When is it appropriate to use the formula F=G/ m1m2 /r2 and when should we use the formula F=ma?
F=ma is Newton's second law, and it is used to find the net force on an object, or the direction of acceleration on that object. The greater the mass of an object, the greater the force needed to accelerate that object. F=G(m1m2)/r^2 is the universal law of gravitation, and it is used to find the gravitational force between two objects. All matter in the universe is attracted to all other matter, and the force of gravity between two objects depends on the mass of each object and the distance between their centers.
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
I think Ken and Joanne would both move towards each other. There is no gravity acting upon them, and the center mass is the same; Ken and Joanna are most likely to move towards each other.
What would be the path of the Moon if somehow all gravitational forces on it vanished to zero?
If all the gravitational forces of the moon vanished to zero, the Moon would move along a linear path.
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?
If only one horse/ two horse pulled and the left rope were tied to a tree, the tension would be the same because according to Newton's third law, it states that in every action there will be an equal and opposite reaction. The forces are equal but acting in opposite in direction. Therefore, the net force is zero.
What physics is involved for a passenger feeling pushed back into the seat of an airplane when it accelerates along the runway during takeoff?
In relation to Newton's Third Law, there is an opposed equal reaction occurring when a passenger is feeling pushed back into their seat when it accelerates along the runway during takeoff. The airplane seat is being pushed forward while the passenger is being pulled backward thus there are two different forces on separate objects making the net force 0.
If you stand next to a wall on a frictionless skateboard and push the wall with a force of 40 N, how hard does the wall push on you? If your mass is 80kg, show that your acceleration is 0.5m/s^2
Newton said that every action has a equal and opposite reaction so pushing the wall is the force of action and the wall reacts with a force of 40 N pushing in the opposite direction. The only force acting is the 40 N of reaction of the wall. If I push against the wall at 40 N the wall with push back with a force of 40 N also. Acceleration=f/m Acceleration=40N/80KG Acceleration= 0.5 m/s^2
Earth and the moon are attracted to each other by gravitational force. Does the more massive earth attract the less massive moon with a force that is greater, smaller, or the same as the force with which the moon attracts earth? (With an elastic band stretched between your thumb and forefinger which is pulled more strongly by the band, your thumb or your forefinger?)
The Earth attracts the Moon with an equal force with which the moon attracts the earth but these forces act in opposite directions. By universal law of gravitation, the force between the moon and the sun will be:F = (G m1 m2/d2) Where m1 & m2 = masses of the earth and the moon respectively.d = distance between the earth and moon. According to the universal law of gravitation and Newton's third law, the force of attraction between these two objects are the same but they act in opposite directions. The distance between the earth and the moon is great enough to make up for the lack of mass the moon has. The main reason the moon doesn't get sucked into the earth, is the gravitational pulls between the two planets are the same, but act in opposite directions!
When do Newton's third law and gravitation are used together? Are they only used together when finding the distance of an object/force between earth?
The Third Law is about the equality and direction of the forces between two objects. The Law of Gravitation allows us to calculate the attraction forces between two objects across distance. The attraction forces between two objects indeed follow the third law, which means the forces acting on the TWO objects are equal in size, opposite in direction.
The planet Jupiter is more than 3-- times as massive as the Earth, so it might seem that a body on the surface of Jupiter would weigh 300 times as much on Earth. But it so happens that a body would weigh scarcely 3 times as much on the surface of Jupiter as on the surface of Earth. Discuss why this is so,using the terms in the equation for gravitational force to guide your thinking.
The equation for gravitational force is F = G (( m 1 X m E)/ (r 2.)) F= is the total attractive force in Newtons m1= is the mass of Jupiter or the other object mE= is the mass of the earth r= is the radius/distance between two masses G= is the gravitational constant The equation and the terms in the equation are important in understanding how to answer the question because it pertains to the attractive force between the gravitational force of Earth and Jupiter. The mass of Jupiter is 300 times than the Earth's mass. Normally that would mean that whatever weighs on earth would be 300 times as much on Jupiter. However, this is not the case because any object on Jupiter is only three times that of an object on earth. The reason that this is the case is because that Jupiter's radius is 10 times larger than the earth, which would mean that the object is significantly further from the center of the Jupiter. This distance reduces the gravity of Jupiter from 300 to 3 because the weakened gravity is affected by a factor of 100.
An apple falls because of the gravitational attraction to Earth. How does the gravitational attraction of Earth to the apple compare? (Does force change when you interchange m1 and m2 in the equation for gravity-m2m1 instead of m1m2?)
The gravitational attraction of Earth to the apple are both the same. According to Newton, every body attracts every other body with a force that, for any two bodies, is directly proportional to the prod-cut of their masses and inversely proportional to the square of the distance between their centers. I think that the force does not change when you interchange m1 and m2 for m2m1.
According to the third law, every action has an opposing equal reaction, how does the net force of the two objects equal to zero if they are acting on the same surface?
When we say net force, we usually mean the net force on ONE given object. The Third Law is about forces on TWO different objects, and they are equal in size and opposite in direction.
When you kick a football, what action and reaction forces are involved? Which force, if either, is greater?
When you're kicking a football the action that is being required is the pushing of your foot to the foot ball and the reaction is the how the football pushes back on the foot. Both forces are equal.
