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Physics Chapter 7 Study.com
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Gravity
Terms in this set (60)
What is the name of the force that keeps an object in circular motion?
Centripetal force
A ball on a string in uniform circular motion has a velocity of 8 meters per second, a mass of 2 kilograms, and the radius of the circle is 0.5 meters. What is the centripetal force keeping the ball in the circle?
256 N
Which of the following is a full definition of uniform circular motion?
It is motion in a circle at a constant speed; this happens because of a centripetal force, a force pointing towards the center of a circle
What is the difference between a scalar and a vector?
Vectors have a direction and scalars do not
An object moving in uniform circular motion has a constant ___________, but a changing ___________.
speed; velocity
Which of the following is a vector quantity?
8 meters/second west
Consider a man walking around a house in a rectangle pattern. He walks 70 feet across the front, 30 feet along the side, 70 feet along the back, and 30 feet along the other side to bring him back to where he began. What is the displacement of the man walking around the house?
There was no displacement as the man ended where he began
Consider a man walking around a house in a rectangle pattern. He walks 70 feet across the front, 30 feet along the side, 70 feet along the back, and 30 feet along the other side to bring him back to where he began. How much distance did this man cover?
200 feet
Which of the following is the best definition of velocity?
The rate of change in displacement with respect to time
Consider a man walking around a house in a rectangle pattern. He walks 70 feet across the front, 30 feet along the side, 70 feet along the back, and 30 feet along the other side to bring him back to where he began. If it took the man 2 minutes to complete the walk, what was his speed?
100 feet/minute
At 4 seconds after starting, a cyclist is traveling 10 m/sec. At 6 seconds, he is traveling 20 m/sec. What is his average acceleration from 4 seconds to 6 seconds?
5 m/sec^2
Average acceleration is calculated by __________.
Dividing the change in velocity by the change in time
An object will experience an acceleration if __________.
All of the answers are correct
Which of the following units would be correct for an acceleration?
m/sec^2
Acceleration is __________.
The rate of change of velocity
If a planet's average distance from the sun is 10 AU, what is its orbital period?
31.6
The time it takes a planet to travel around the sun one time is known as the:
Orbital period
A curve surrounding two points, called foci, such that the total distance from one focus to a point on the ellipse and back to the other focus is constant for every point on the curve is called:
An ellipse
If a planet's orbital period is 10 years, what is its average distance from the sun?
4.64 au
Kepler's Second Law states:
A line drawn from a planet to the sun always sweeps over equal areas in equal intervals of time
What is Newton's Law of Gravitation?
It says that every object in the universe attracts every other object
Object A has a mass of 3 x 10^10 kilograms, and object B has a mass of 8 x 10^10 kilograms. If they are 8,000 meters apart, what is the gravitational attraction between them? (G = 6.67 x 10^-11)
2500 N
What kind of relationship does gravity follow with distance?
An inverse-square relationship
If the distance between two objects is doubled, and the mass of one of the objects is doubled, what happens to the gravitational force?
It reduces to a half
If you increase the distance between two objects by a factor of three, what happens to the force between them?
It reduces to a ninth
What is the definition of centripetal force?
A force directed towards the center of a circle that keeps an object moving in a circle
A car of mass 1500 kg, moves in a circle of 30 m/s. If the circle has a radius of 8 meters, what is the size of the frictional force that is moving the car in the circle?
168750 newtons
Why do you feel a centrifugal force if it isn't real?
Because your body wants to keep going in a straight line, as explained by Newton's 1st Law
For a satellite in orbit, what force provides the centripetal force that keeps it moving in a circle?
Gravitational force
When you're whirling a ball on a strong, what specific force keeps it moving in a circle? (What force would you mark on a force diagram of the situation?)
The tension force
A metal bar is positioned near the Sun. If the mass of the metal bar is 20,000 kilograms, the mass of the Sun is 2 x 10^30 kilograms, the distance to the nearside of the bar from the Sun is 100,000 meters and the length of the bar is 300 meters, what is the force of gravity between the Sun and the bar?
266, 001, 994, 017, 946 newtons
Which of the following is an assumption of Newton's Universal Law of Gravitation that doesn't ever apply to an extended object?
Masses can be taken as point masses
Which of these describes the basic idea of how calculus is used to find the gravitational force due to an extended object?
Breaking an object into mass elements, and integrating to get the total of the forces on all those elements
What is Newton's Law of Universal Gravitation in words?
Every body in the universe attracts every other body, with a force that is proportional to the product of their masses, and inversely proportional to the square of the distance between them
What is an extended object?
An object that is not spherical, or uniform in shape, and cannot be treated as a point mass
If a car is rolling naturally downhill without the engine running, what energy transfer is happening?
Gravitational potential energy is changing into kinetic energy
You lift a 3kg dumbbell from the ground until it is above your head at a height of 1.5 meters. How much energy did you use in the process? (Assume that you're not a space alien, and your gym is on Earth.)
44 joules
How do we know that gravitational potential energy exists?
Because when you drop a ball, it starts to move, and this energy has to come from somewhere
If all of the objects have around the same mass, which of the following objects has the most gravitational potential energy?
A ball stuck on the roof of a two-story house
A 10 kg bowling ball is lifted from the ground to a height of 1 meter. Assuming the bowling alley is on Earth, how much gravitational potential energy does it now have?
98 joules
What is work in physics?
The energy transferred from one type into another type when a force is applied causing an object to move a distance
The force applied to an object is given by the equation F = 3x^2 + 2x. If the total displacement is 2 meters, how much work is done in the process?
12 joules
The force applied to an object is given by the equation F = 2x. If the total displacement is 4 meters, how much work is done in the process?
16 joules
The force applied to an object is given by the equation F = 6x + 1. If the total displacement is 5 meters, how much work is done in the process?
80 joules
If you were given a force-displacement graph, how would you figure out the work done in the process?
Find the area under the graph
A planet is orbiting its star at a maximum radius of 1.2 x 10^7 meters. If the mass of the star is 2 x 10^30 kg, and the current radius is 0.9 x 10^7 meters, what is the velocity of the orbit?
4.3 x 10^6 meters per second
In general, what are Kepler's Laws?
A series of laws that describe the motion of orbiting bodies no matter the shape of the orbit
Which of the following orbital eccentricities in not an elliptical orbit?
1
What is an elliptical orbit?
An orbit between a circle and a parabola in shape (but not including a parabola)
A planet is orbiting its star at a maximum radius of 1.2 x 10^7 meters. If the mass of the star is 2 x 10^30 kg, what is the time period of the orbit?
22.6 seconds
Which planet is the most eccentric in its orbit? (Not counting dwarf planets like Pluto)
Mercury
What is the eccentricity of a parabolic trajectory?
1
What does eccentricity measure?
How non-circular the orbit of a body is
What is the eccentricity of a circular orbit?
0
If the distance between the two foci in an orbit is 4 AU, and the length of the major axis is 9 AU, what is the eccentricity of the orbit?
0.444
Is motion in a vertical circle 'uniform circular motion'? Why?
No, because the velocity is faster at the bottom than it is at the top
What is uniform circular motion?
Motion in a circle at a constant speed
A ball on a string moving in a vertical circle has a mass of 8 kilograms. If the radius of the circle is 0.5 meters, and the velocity at the bottom of the circle is 6 m/s, what is the ball's velocity at the top of the circle?
4.05 m/s
A ball on a string is whirled in a vertical circle. If the tension in the string at the top of the circle in 10 newtons, and the ball weighs 2 kilograms, what is the tension in the string at the bottom of the circle?
127.6 newtons
What is the centripetal force equal to at the top of a vertical circle?
Force of tension + mg
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