Physics Final- Chapters 6-10

Matter

-Substance we can see, smell, and feel -Occupies space

What would happen to Earth if the Sun became a black hole? a. It would break away from the attraction of the Sun b. It would be pulled into the Sun c. It would become a black hole too d. None of the above

D. None of the above Letting the equation for gravity guide our thinking, we see that no mass, chagnes, no distance from center to center changes, so there would be NO change in force between the shrunken Sun and Earth

Conservation of Energy

Energy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes.

Conservation of angular momentum

If no external net torque acts on a rotating system, the angular momentum of that system remains constant.

Bouncing

Impulses are generally grater when objects bounce.

Gravitational field

an alteration of space around Earth (or any object with mass) -it decreases to zero at the center -outside a planet, it decreases to zero at infinity. (you are farther from planet)

Wormhole

an enormous distortion of space-time, but instead of collapsing toward an infinitely dense point, the wormhole opens out again in some other part of the universe, or other universe. -no wormholes have been found

Impulse

product of force and time impulse= Ft -A brief force applied over a short itme interval produces a smaller change in momentum than the same force applied over a longer time interval. -If you push with the same force for twice the time, you impart twice the impulse and produce twice the change in momentum.

Fast-moving projectiles

satellites; falls around Earth rather than into it -circular satellite orbits; constant, only direction changes, beyond Earth's atmosphere where there is no air

Angular momentum

the "inertia of rotation" of rotating objects is called angular momentum. -angular momentum=rotational inertia x angular velocity

Center of mass

the average position of all the mass that makes up the object

Tangential speed

the distance traveled by a point on the rotating object divided by the time taken to travel that distance

Rotational speed

the number of rotations or revolutions per unit of time. -all parts of a rigid merry-go-round or turntable turn about the axis of rotation i nthe same amount of time. Tangential speed= radical distance x rotational speed

Newtonian synthesis

the same set of laws apply to bith celestial and terrestrial objects

Centripetal force

when a car rounds a curve, the centripetal force prevents it from skidding off the road -if the road is wet, or if the car is going too fast, the centripetal force is insufficient to prevent skidding off the road

Energy for life

-Body is a machine, so it needs energy. -Our cells feed on hydrocarbons that release energy when they react with oxygen (like gas burned in a car) -There is more energy stored in the food than i nthe products after metabolism.

Universal Law of gravitation

-Everything pulls on everything else -Every body attracts every other body with a force taht is directly proportional to the square of the distance separating them. -F~ m1m2/d^2 where m is the mass of the objects and d is the distance between their centers

Impulse Changes momentum pt. 2

-In jumping, bend your knees when your feet make contact with the ground bc the extension of time during momentum decrease reduces the force on you. -In boxing, ride with the punch. -Decreasing momentum over a short time- short time interval produces large force.

Recycled Energy

-Re-employment of energy taht otherwise would be wasted. -Edison used heat from his power plant in New Your City to heat buildings. -Typical power plants waste about 30% of their energy to heat because they are built away from buildings and other places that use heat.

Momentum

-a property of moving things -inertia in motion -a moving boulder has more momentum than a stone rolling at the same speed momentum= mass x velocity

Principles of a machine

-conservation of energy concept: work input = work output -input force x input distance= output force x output distance

Machine

-device for multiplying forces or changing the direction of forcesj -cannot create energy but can transform energy from one form to another, or transfer energy from one location to another -cannot multiply work or energy

Mechanical energy

-due to position or motion, or both -there are two forms: potential and kinetic

Kinetic Energy

-energy of motion -depends on the mass of the object and square of its speed -kinetic speed=1/2 x mass x speed x speed -If object speed is doubled, kinetic energy is quadrupled.

Work

-involves force and distance -W=Fd -two things occur when this is done... application of force and movement of something by that force -units are newton-meter(Nm) or joule (J)

Power

-measure of how fast work is done -power=work done/time interval -units are watts

Energy

-mover of substances -both a thing and a process -observed when it is being transferred or being transformed -a conserved quantity

Pulley

-operates like a lever with equal arms-changes the direction of the input force -operates as a system of pulleys (block and tackle) -multiplies force

The inverse-square law

-relates the intensity of an effect to the inverse-square of the distance from the cause -intensity=1/distance^2 -for increases in distance, there are decreases in force -even at great distances, force approaches but never reaches zero.

Lever

-simplest machine -rotates on a point of support called the fulcrum -allows small force over a large distance and large force over a short distance

Projectile motion

-without gravity, a tossed object follows a straight-line path. -with gravity, the same object tossed at an ange follows a curved path -horizontal component of velocity doesn't change (when air drag is negligible) -vertical positions become farther apart with time -parabolic trajectory -without air resistance, time for a projectile to reach max. height is the same for it to return to initial height

A certain machine is 30% efficient. This means the machine will convert a. 30 % of the energy input to useful work- 70% of the energy input will be wasted. b. 70% of the energy input to useful work- 30% of the energy input will be wasted. c. Both of the above d. None of the above

A. 30% of the energy input to useful work- 70% of the enrgy input will be wasted.

Suppose you take a sharper turn than before and halve the radius, by what factor will the centripetal force need to change to prevent skidding? a. Double b. Four times c. Half d. One-quarter

A. Double Because the term for "radius" is in the denominator, if you halve the radius, the centripetal force will double.

Suppose by pulling the weight inward, the rotational inertia of the man reduces to half its value. By what factor would his angular velocity change? a. Double b. 3x c. Half d. One-quarter

A. Double IF you halve the rotational inertia, to keep the angular momentum constant, the angular velocity would double.

Suppose you are swirling a can around and suddenly decide to pull the rope in halfway; by what factor would the speed of the can change?

A. Double No external torque acts with inward pull, so angualr momentum is conserved. Half radius means speed doubles.

Does a car hoisted for repairs in a service station have increased potential energy relative to the floor? a. Yes b. No c. Sometimes d. Not enough information

A. Yes If the car were twice as heavy, its increase in potential energy would be twice as great.

When a satellite travels at a constant speed, the shape of the its path is a. a circle b. an ellipse c. an oval that is almost elliptical d. a circle with a square corner

A. a circle

If the mass of one planet is somehow doubled, the force of gravity between it and a neighboring planet a. doubles b. quadruples c. reduces by half d. reduces by one-quarter

A. doubles Let the equation guide your thinking: Note that if one mass doubles, then the force between them doubles.

When no air resistance acts on a fast-moving baseball, its acceleration is a. downward, g. b. a combination of constant horizontal motion and accelerated downward motion. c. opposite to the force of gravity d. centripetal

A. downward, g.

Newton's most celebrated synthesis was and is of a. earthly and heavenly laws b. weight on Earth and weightlessness in outer space. c. masses and distances. d. the paths of tossed rocks and the paths of satellites

A. earthly and heavenly laws This synthesis provided hope that other natural phenomena followed universal laws and ushered in the "Age of Enlightenment"

When an elevator accelerates upward, your weight reading on a scale is a. greater b. less c. zero d. the normal weight

A. greater The support force pressing on you is greater, so you weigh more.

The force of gravity between two planets depends on their a. masses and distance apart b. planetary atmospheres c. rotational motions d. all of the above

A. masses and distance apart The equation for gravitational force, cites only masses and distances as variables. Rotation and atmospheres are irrelevant.

When you toss a projectile sideways, it curves as it falls. It will be an Earth satellite if the curve it makes a. matches the curved surface of Earth b. results in a straight path c. spirals out indefinitely d. none of the above

A. matches the curved surface of the Earth For an 8-km tangent, Earth curves downward 5m. Therefore, a projectile traveling horizontally at 8 km/s will fall 5m in that time, and follow the curve of the Earth

The universal gravitational constant, G, which links force to mass and distance, is similar to the familiar constant a. pi b. g c. acceleration due to gravity d. speed of uniform movement

A. pi Just as pi relates the circumferences of a circle to its diameter, G relates force to mass and distance.

Work is done in lifting a barbell. How much work is done in lifting a barbell that is twice as heavy the same distance? a. twice as much b. half as much c. the same d. depends on the speed of the lift

A. twice as much This is in accord with work=force x distance. Twice the force for the same distance means twice the work done on the barbell.

Centrifugal force

Although centripetal force is center directed, an occupant inside a rotating system seems to experience an outward force. -means "center-fleeing" or "away from the center"

Suppose the potential energy of a drawn bow is 50 joules and the kinetic energy of the shot arrow is 40 joules. Then.. a. energy is not conserved b. 10 joules go to warming the bow c. 10 joules go to warming the target d. 10 joules are mysteriously missing

B. 10 joules go to warming the bow The total energy of the drawn bow, which includes the poised arrow, is 50 joules. The arrow gets 40 joules and the remaining 10 joules warms the bow- still in the initial system.

Neglecting air drag, a ball tossed at an angle of 30 degrees with the horizontal will go as far downrange as one that is tossed at the same speed at an angle of a. 45 degrees b. 60 degrees c. 75 degrees d. none of the above

B. 60 degrees Same initial-speed projectiles have the same range when thier launching angles add up to 90 degrees.

A hoop and a disk are released from the top of an incline at the same time. Which one will reach the bottom first? a. Hoop b. Disk c. Both together d. Not enough info.

B. Disk Hoop has larger rotational inertia, so it will be slower in gaining speed.

Suppose you double the speed at which you round a bend in the curve, by what factor must the centripetal force change to prevent you from skidding? a. Double b. Four times c. Half d. One-quarter

B. Four times Because the term for "tangential speed" is squared, if you doublt the tangential speed, the centripetal force will be double squared, which is four times.

A fast-moving car hitting a haystack or a cement wall produces vastly different results. 1. Do both experience the same change in momentum? 2. Do both experience the same impulse? 3. Do both experience the same force? a. Yes for all three b. Yes or 1 and 2 c. No for all three d. No for 1 and 2

B. Yes for 1 and 2 Although stopping the momentum is the same whether done slowly or quickly, the force is vastly different. Be sure to distinguish among momentum, impulse, and force.

When the force that produces an impulse acts for twice as much time, the impulse is a. not changed b. doubled c. quadrupled d. halved

B. doubled

When the speed of an object is doubled, its momentum a. remains unchanged in accord with the conservation of momentum b. doubles c. quadruples d. decreases

B. doubles

Freight car A is moving toward identical freight car B that is at rest. When they collide, both freight cars couple together. Compared with the initial speed of freight car A, the speed of the coupled freight cars is a. the same b. half c. twice d. none of the above

B. half After the collision, the mass of the moving freight cars has doubled. Can you see their speed is half the initial velocity of freight car A?

When an elevator accelerates downward, your weight reading is a. greater b. less c. zero d. the normal weight

B. less The support force pressing on you is less, so you weigh less. Question: would you weigh less in an elevator that moves downward at constant velocity?

When a projectile achieves escape speed from Earth, it a. forever leaves Earth's gravitational field b. outruns the influence of Earth's gravity, but is never beyond it c. comes to an eventual stop, returning to Earth at some future time d. all of the above

B. outruns the influence of Earth's gravity, but is never beyond it. (Satellites do this when we go to Moon, Mars, and beyond.)

If the masses of two planets are each somehow doubled, the force of gravity between them a. doubles b. quadruples c. reduces by half d. reduces by half

B. quadruples Note that both masses double. Then, double x double = quadruple

You do work when pushing a cart with a constant force. If you push the cart twice as far, then the work you do is a. less than twice as much b. twice as much c. more than twice as much d. zero

B. twice as much

In an ideal pulley system, a woman lifts a 100-N crate by pulling a rope downward with a force of 25 N. For every 1-meter length of rope she pulls downward, the crate rises a. 50 centimeters b. 45 meters c. 25 meters d. None of the above

C. 25 centimeters Work in = work out; Fd in= Fd out. One-fourth of 1m =25 cm

A ladybug sits halfway between the rotational axis and the outer edge of the turntable. When the turntable has a rotational speed of 20 RPM and the bug has a tangential speed of 2cm/s, what will be the rotational and tangential speeds of her friend who sits at the outer edge? a. 1cm/s b. 2cm/s c. 4cm/s d. 8cm/s

C. 4cm/s Rotational speed of both bugs is the same, so if radial distance doubles, tangential speed also doubles.

If you weigh yourself in an elevator, you'll weigh more when the elevator a. moves upward b. moves downward c. accelerates upward d. all of the above

C. accelerates upward The support provided by the floor of an elevator is the same whether the elevator is at rest or moving at constant velocity. Only accelerated motion affects weight.

A job can be done slowly or quickly. Both may require the same amount of work, but different amounts of a. energy b. momentum c. power d. impulse

C. power Power is the rate at which work is done

The velocity of a typical projectile can be represented by horizontal and vertical components. Assuming negligible air resistance, the horizontal component along the path of the projectile a. increases b. decreases c. remains the same d. Not enough info.

C. remains the same Since there is no force horizontally, no horizontal acceleration occurs.

When the elevator cable breaks, the elevator falls freely, so your weight reading is a. greater b. less c. zero d. the normal weight

C. zero There is still a downward gravitational force actig on you, but gravity is not felt as weight because there is no support force, so your weight is zero.

Suppose the girl on the left suddenly is handed a bag of apples weighing 50 N. Where should she sit in order to balance, assuming the boy does not move? a. 1m from pivot b. 1.5m from pivot c. 2m from pivot d. 2.5m from pivot

D. 2.5 m from pivot She should exert same torque as before. Torque=leer arm x force =3 m x 250 N =750 Nm 750 Nm=new lever arm x 250N New lever arm =750 Nm/250 N= 2.5 m

A moving object has a. momentum b. energy c. speed d. All of the above

D. All of the above Energy motion is called kinetic energy.

Consider a problem that asks for the distance of a fast-moving crate sliding across a factory floor and then coming to a stop. The most useful equation for solving this problem is.. a. F=ma b. Ft=change in mass x velocity c. KE = 1/2mv^2 d. Fd= change in 1/2mv^2

D. Fd=change in 1/2mv^2 The work-energy theorem is the physicist's favorite stating point for solving many motion-related problems.

The work done in bringing a moving car to a stop is the force of tire friction x stopping distance. If the initial speed of the car is doubled, the stopping distance is a. actually less b. about the same c. twice d. None of the above

D. None of the above Twice the speed means four times the kinetic energy and four tiems the stopping distance.

Potential Energy- Gravitational

Equal to the work done (force required to move it upward x the vertical distance moved against gravity) in lifting it. - potential energy =mass x acceleration due to gravity x height - =mgh

Collisions

For all collisions in the absence of external forces, net momentum before collision equals net momentum after collision. (net mv)before = (net mv) after

Work-energy theorem

Gain or reduction of energy is the result of work. -work =change in kinetic energy Doubling speed of an object requires 4 times the work. -Applies to decreasing speed; reducing the speed of an object or bringing it to a halt

Conservation of momentum

In the absence of an external force, the momentum of a system remains unchanged. -When no external force is present, no external impulse is present, and no change in momentum is possible.

Elastic collision

Occurs when colliding objects rebound without lasting deformation or any generation of heat. -Single car moving at 10 m/s collides with another car of the same mass, m, at rest. (m x 10)before = (2m x V) after V = 5m/s

Inelastic collision

Occurs when colliding objects result in deformation and/or the generation of heat.

Ocean tides

Ocean tides are caused due to the gravitational attraction of the moon. -Unequal tugs on Earth's oceans causes a stretching effect that produces a pair of ocean bulges.

Efficiency

Percentage of work put into a machine that is converted into usedful work output. - efficiency = useful energy output/ total energy input

Why is it better for an out of control car to hit a haystack rather than a cement wall?

Same impulse either way, but extension of hitting time reduces the force.

Kinetic Energy and Momentum compared

Similarities: Both are properties of moving things. Differences: -Momentum is a vector quantity and therefore is directional and can be canceled. -Kinetic energy is a scalar quantity and can never be canceled. Velocity dependence -Momentum depends on velocity -Kinetic energy depends on the square of velocity.

Potential Energy

Stored energy held in readiness with a potential for doing work. -due to elevated position -stretched bow or rubber band sling shot

Impulse changes momentum

The greater the impulse exerted on something, the greater the change in momentum. -Apply the greatest force for as long as possible and you extend the time of contact. (golfer swings a club and follows through) -Decreasing momentum over a long time, extend the time during which momentum is reduced.

Kepler's second law of Planetary motion

The line from the sun to any planet sweeps out equal areas of space in equal time intervals.

Kepler's first law of Planetary Motion

The path of each planet around the Sun is an ellipse.

Kepler's third law of Planetary motion

The square of the orbital period of a planet is directly proportional to the cube of the average distance of teh planet from the Sun (for all planets).

Torque

The tendency of a force to cause rotation -depends on 3 factors; magnitude of force, direction in which it acts, and the point at which it is applied. - torque= lever arm x force -the lever arm depends on where the force is applied and the direction in which it acts.

Energy Conservation and Satellite motion

When satellite gains altitude and moves against gravitational force, its speed and KE decrease and continues to the apogee (farthest point). Past the apogee, satellite moves in the same direction as the force component and speed and KE increase.

Black hole

When the star becomes so small and the gravitational force at the surface becomes so large that even light cannot escape the surface; anything in its vicinity will be attracted by warped space-time and lost forever

The speed of a satellite in an elliptical orbit a. varies b. remains constant c. acts at right angles to its motion d. all of the above

a. Varies A satellite in an elliptical orbit half the time recedes from Earth and loses speed and half the time approaches Earth and gains speed.

Must a car with momentum have kinetic energy? a. Yes, due to motion alone b. Yes when motion is non accelerated c. Yes, because speed is scalar and velocity is a vector quantity d. No

a. Yes, due to motion alone. Acceleration, speed being a scalar, and velocity being a vector quantity are irrelevant. Any moving object has both momentum and kinetic energy.

If you push against a stationary brick wall for several minutes, you do no work a. on the wall b. at all c. Both of the above d. none of the above

a. on the wall You may do work on your muscles, but not on the wall.

Rotational inertia

an object rotating about an axis tends to remain rotating about the same axis at the same rotational speed unless interfered with by some external influence. -the property of an object to resist changes in its rotational state of motion is called rotational inertia depends upon mass of object, and distribution of mass around axis of rotation. -The greater the rotational inertia, the harder it is to change its rotational state.

Projectile

any object that moves through the air or space under the influence of gravity, continuing in motion by its own inertia

Center of gravity

the average position of weight distribution -to determine, suspend the object from a point and draw a vertical line from suspension point. repeat after suspending from another point. The center of gravity lies where the two lines intersect -important for stability; in its stable equilibrium, it will balance

Circular motion

when an object turns about an internal axis, it is undergoing circular motion or rotation. -characterized by two kinds of speeds: tangential (linear) speed and rotational (or circular) speed