Physics 114

A 10-kilogram block is pushed across a horizontal surface with a horizontal force of 20 N against a friction force of 10 N. The acceleration of the block in meters per second per second is

1

kinetic energy equation

1/2 x mass x speed x speed

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

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

A2 A rock is thrown vertically into the air. At the top of its path, its acceleration in meters per second per second is

10 m/s

A2 A 10-kg brick and a 1-kg book are dropped in a vacuum. The force of gravity on the 10-kg brick is

10 times as much.

A 2A jumbo jet has a mass of 100,000 kg. The thrust for each of its four engines is 50,000 N. What is the jet's acceleration in meters per second per second when taking off?

2

A2A horse gallops a distance of 10 kilometers in a time of 30 minutes, its average speed is

20 km/h

A2an object at rest near the surface of a distant planet starts to fall freely. if the acceleration there is twice that of the earth, its speed one second later would be

20 m/s

A2 A ride on a roller-coaster car containing 6 passengers takes 3 minutes. Neglecting friction, a similar ride with 12 passengers aboard would take

3 minutes.

A2 A 2000-kg car experiences a braking force of 10,000 N and skids to a stop in 6 seconds. The speed of the car just before the brakes were applied was

30 m/s

A2 if a rocket initially at rest accelerates at a rate of 50 m/s^2 for one minute, its speed will be

3000m/s

Two people, one twice as massive as the other, attempt a tug-of-war with 12 meters of massless rope on frictionless ice. After a brief time, they meet. The heavier person slides a distance of

4 m

A1 A man weighing 800 N stands at rest on two bathroom scales so that his weight is distributed evenly over both scales. The reading on each scale is

400 N.

A2 An object is pulled northward by a force of 10 N and at the same time another force of 15 N pulls it southward. The magnitude of the net force on the object is

5 N

A2 When a person stands at rest with both feet on a scale, it reads 500 N. When they gently lifts one foot, the scale reads

500 N

A person is attracted toward the center of Earth by a 500-N gravitational force. The Earth is attracted toward the person with a force of

500 N.

A2 A 10-N falling object encounters 4 N of air resistance. The net force on the object is

6 N

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

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 energy input will be wasted.

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 centimeters. C.25 centimeters. D.None of the above.

C.25 centimeters. Explanation:Work in = work out; Fdin = Fdout. One-fourth of 1 m = 25 cm.

the work is dine in bringing a moving car to 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 times the stopping distance

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

Fd=^1/2mv2

A2 An apple falls from a tree and hits the ground 5 meters below. It hits the ground with a speed of about

Given: displacement=S=5m initial velocity=u=0 acceleration=a=10 m/s using position-velocity relation v= ________________________ v | 0^2 + 2 x 10 x 5 v=10 m/s

A2At one instant a heavy object in air is moving upward at 50 meters per second. One second later its speed is approximately

Let v be the speed of the object after one second Using the kinematic equation v=u-gt v=50-(9.8 x 1) =40.2 m/s

energy

Mover of substances both a thing and a process observed when it is being transferred or being ransformed a conserved quantity

A1 When a rocket ship accelerating in outer space runs out of fuel, it

No longer accelerates The acceleration of a rocket ship in outer space is due to the engine's thrust force

A2 It takes 6 seconds for a stone to fall to the bottom of a mine shaft. How deep is the shaft?

Now, the position of the stone in time is given by the following equation. Y=Yo+Voy∗t+12∗ay∗t2Y=Yo+Voy∗t+12∗ay∗t^2 h=1/2 x 9.8(m/s^2) x (6.0s)^2 = 176.4 About 180 m

Efficency

Percentage of work put into a machine that is converted into useful work output• In equation form: Efficiency =useful energy output /total energy input

Recycled energy

Re-employment of energy that otherwise would be wasted.•Edison used heat from his power plant in New York 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.

A1 Eratosthenes learned about the position of the sun on June 22 by

Setting Up sticks at both Syene and Alexandria

A car traveling at 100 km/hr strikes an unfortunate bug and splatters it. The force of impact is greater on the car. the same for both. greater on the bug

The same for both

work is done in lifting a barbell. how much work is done in lifting a barbell that is twice as heavy the same distance?

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

_______as much work is done in lifting 2 loads 1 story high versus lifting 1 load the same vertical distance

Twice as much work is done in lifting 2 loads 1 story high versus lifting 1 load the same vertical distance Reason: force needed to lift twice the load is twice as much

A2 If a projectile is fired straight up at a speed of 10 m/s, the total time to return to its starting position is about

Using the equation v-u=gt 0-10m/s=(-9.8)t t=1.0204 About 1 second

equation for work

W=Fd

A2 A ball tossed vertically upward rises, reaches its highest point, and then falls back to its starting point. During this time the acceleration of the ball is always

When a ball is tossed vertically upward then it moves under the force of gravity and there is no other force acting on ball. Drag acting on ball is assumed insignificant . During upward motion, ball moves against the gravity and its velocity keep on decreasing till it becomes zero at maximum point of the trajectory. So The velocity is zero, the acceleration is directed downward, and the force of gravity acting on the ball is directed downward.

must a car with momentum have kinetic energy

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.

A1 In science, a theory is

a synthesis of a large body of well-tested knowledge.

A2 The mass of a pet turtle that weighs 10 N is

about 1 kg

A1 A package falls off a truck that is moving at 30 m/s. Neglecting air resistance, the horizontal speed of the package just before it hits the ground is

about 30 m/s.

If an object of constant mass experiences a constant net force, it will have a constant

acceleration.

Science is a body of knowledge that describes order in nature. condenses knowledge into testable laws. is an ongoing activity of humans. all of the above tare correct. None of the above choices are correct

all of the above are correct.

A1 Science, art, and religion do not contradict one another because

all three have different domains

A1 According to Newton's law of inertia, a railroad train in motion should continue going forever even if its engine is turned off. We never observe this because railroad trains

always have forces that oppose their motion.

two things that occur whenever work is done

application of force movement of something by that force

An archer shoots an arrow. Consider the action force to be the bowstring against the arrow. The reaction to this force is the

arrow's push against the bowstring.

similarities between momentum and kinetic energy

both are properties of moving things

principle of a machine

conservation of energy concept: work input=work output input force x input distance = output force x output distance (force x distance)=(Force x distance)

conservation of energy, a situation to ponder

consider the system of a bow and arrow. In the drawing of the bow we do work on the system and give it potential enrgy. WHen the bowstring is released, most of the potential enrgy is transferred to the arrow as kinetic energy, and some as heat to the bow

A1 If no external forces are acting on a moving object, it will

continue moving at the same velocity.

A1 Science is a body of knowledge that

describes order in nature. condenses knowledge into testable laws. is an ongoing activity of humans.

machine

device for multiplying forces or changing the direction of forces 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

A2 the two measurements necessary for calculating average speed are

distance and time

Law of 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

kinetic energy

energy of motion depends on the mass of the object and square of its speed

A1 Whereas Aristotle relied on logic in explaining nature, Galileo relied on

experiment.

A1 Whirl a rock at the end of a string and it follows a circular path. If the string breaks, the tendency of the rock is to

follow a straight-line path.

A player hits a ball with a bat. The action force is the impact of the bat against the ball. The reaction to this force is the

force that the ball exerts on the bat.

work energy theorem

gain or reduction of energy is the result of work in equation form: work =change in kinetic energy doubling speed of an object requires 4 times the work

A1 The scientific method is most effective in

gaining, organizing, and applying new knowledge.

A1 The scientist to first introduce the concept of inertia was

galileo

A coconut and a feather fall from a tree through the air to the ground below. The amount of air-resistance force is

greater on the coconut.

A1 In science, an educated guess is a

hypothesis

A1 If your automobile runs out of fuel while you are driving, the engine stops but you do not come to an abrupt stop. The concept that most explains why is

inertia.

work

involves force and distance is force x distance

mechanical energy

is due to position or to motion or both

For an action force, there must be a reaction force that

is exactly equal in magnitude.

unit of power

joule per second, called watt after James Watt developer of the steam engine 1 joule/second=1 watt 1 kilowatt=1000 watts

Two tennis balls fall through the air from a tall building. One of them is filled with lead pellets. The ball to reach the ground first is the

lead-filled ball.

A2 A kilogram is a measure of an object's

mass

A2 Compared to a 1-kg block of solid iron, a 2-kg block of solid iron has twice as much

mass volume inertia

potential energy equation form

mass x acceleration due to gravity x height

A1 In science, facts

may change

power

measure of how fast work is done

velocity dependence

momentum depends on velocity kinetic energy depends on the square of velocity example: an object moving with twice the velocity of another with the same mass, has twice the momentum but 4 times the kinetic energy

difference between momentum and kinetic energy

momentum is a vector quantity and therfore can be directional and can be canceled kinetic energy is a scalar quantity and can never be canceled

A2twelve seconds after starting from rest, an object falling freely will have a speed of

more that 100 m/s

A1 An object in mechanical equilibrium is an object

moving with constant velocity. at rest. having no acceleration.

unit of work

newton-meter Nm or joule J

pulley

operates like a lever eith equal arms-changes the direction of the input force ex. this pulley arrangement can allow a load to be lifted with half the input force

two forms of mechanical energy

potential kinetic

A job can be done slowly or quickly both may require the same amount of work, but different amounts of

power

The force exerted on the tires of a car to directly accelerate it along a road is exerted by the

road

lever

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

potential energy

stored energy held in readiness with a potential for doing work

matter

substance we can see, small, and feel occupies space

Sources of energy

sun, fuel cell, concentrated energy, Dry-rock geothermal power

A2 Strange as it may seem, it is just as hard to accelerate a car on a level surface on the moon as it is here on the Earth. This is because

the mass of the car is independent of gravity.

A1 A sheet of paper can be withdrawn from under a container of milk without toppling it if the paper is jerked quickly. This best demonstrates that

the milk carton has inertia.

The attraction of a person's body toward Earth is called weight. The reaction to this force is

the person's body pulling on the Earth.

A feather and a coin will have equal accelerations when falling in a vacuum because

the ratio of each object's weight to its mass is the same.

A2 drop a rock from a 5-m height and it accelerates at 10 m/s^2 and strikes the ground 1 s later. Drop the same rock from a height of 2.5 m and its acceleration of fall is about

the same amount

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

twice as much

______ as much work is done in lifting a load 2 stores instead of 1 story

twice as much work is done in lifting a load 2 stories instead of 1 story Reason: distance is twice as great

A2While an object near the earth's surface is in free fall, its

velocity increases A free fall -state of falling where the only force acting on the object is the force due to gravity. -An object in free fall experiences a constant acceleration called the acceleration due to gravity. The value of this acceleration is: g=9.8m/s2g=9.8m/s2 The acceleration of an object is described as the rate of change of velocity of the object. A constant acceleration in the downward direction implies a continuously increasing velocity of the object in the downward direction.

A2 A person leans over the edge of a cliff and throws a rock upward at 4.9 m/s. Neglecting air resistance, two seconds later the rock's speed is

vi=4.9 m/s initial speed of the rock t=2 s time g=9.8 m/s^2 acceleration due to gravity For this problem, we will set the positive y-axis to be directed upwards. Since, acceleration due to gravity is directed downwards then it will be designated with a negative sign. Solving for the final speed of the rock after 2 seconds, vf=vi+at=vi−gt=4.9ms−9.8m/s2(2 s)=−14.7m/s The negative sign implies that the rock is going down 2 seconds later.

A1 A scientific hypothesis may turn out to be right or it may turn out to be wrong. If it is a valid hypothesis, there must be a test for proving it

wrong

does a car hoisted fro repairs in a service station have insreased potential energy relative to the floor

yes if the car were twice as heavy, its increase in potential energy would be twice as great

A2a car maintains a constant velocity of 100 km/hr for 10 seconds. During this interval its acceleration is

zero