Exam #1 (Chapters 1-6)

Calculate the acceleration of a bus that goes from 10 km/h to a speed of 50 km/h in 10 seconds.

((10 km/h)-(10 km/h))/10 seconds = 4 km/hs

Calculate the distance you will travel if you maintain an average speed of 10 km/h for one half-hour.

(10 km/h)(1/2h) = 5km

Calculate the instantaneous speed of an apple that falls freely from a rest position and accelerates at 10 m/s^2 for 1.5 seconds.

(10 m/s^2)(1.5s) = 15 m/s

Susie Small finds she weights 300 N. Calculate her mass.

(300N)/(10N/kg) = 30 kg

Calculate the speed of a skateboarder who accelerates from rest for 3 seconds down a ramp at an acceleration of 5 m/s^2.

(5m/s^2)(3s) = 15 m/s

Compared with a 1-kg block of solid iron, a 2-kg block of solid iron has the same

*Not volume, mass, or weight

Which contains more atoms: 1 kg, of lead or 1 kg of aluminum?

1 kg of Al because it's lighter and needs more to = 1 kg of lead

A coconut drops from a tree and hits the ground in 1.5 seconds. Calculate how far it falls.

1/2(10m/s)(1.5)^2 = 11.25m

The force of friction on a sliding object is 10 N. The applied force needed to maintain a constant velocity is

10 N

What will be the kinetic energy of a pile driver ram when it undergoes a 10-kJ decrease in potential energy?

10 kJ

Two 100 N weights are attached to a spring scale as shown. Does the scale read 0 N, 100 N, or 200 N, or does it show some other reading?

100 N

A nucleons with an atomic number of 20 and a mass number of 32 must have

12 neutrons AND 12 protons

The sketch shows a painter's scaffold in mechanical equilibrium. The person in the middle weighs 250 N, and the tension in each rope are 200 N. What is the weight of the scaffold?

150 N

Calculate the horizontal force that must be applied to produce an acceleration of 1.8g for a 1.2-kg puck on a horizontal friction-free air table

2.16

A horse gallops a distance of 10 kilometers in a time of 30 minutes. It's average speed is

20 km/h

10 seconds after starting from rest, a car is moving 40 m/s. What is the car's acceleration?

4.0m/s^2

An object is pulled northward with a force of 10 N and southward with a force of 15 N. The magnitude of the net force on the object is

5 N

Starting from rest, the distance a freely falling object will fall in 10 s is about

500 m

Calculate your average speed if you run 50 meters in 10 seconds.

50m/10s = 5m/s

An object is in free fall. At one instant, it travels at a speed of 50 m/s. Exactly 1 s later, its speed is about

60 m/s

Compared with some original speed, how much work must the brakes of a car supply to stop a car that is moving four times as fast? How will the stopping distance compare?

A four times as fast car has 16 times as much KE and will require 16 times as much work to stop, and 16 times as much stopping distance.

A. Calculate the acceleration of a 2-kg block on a horizontal friction-free air table when you exert a horizontal net force of 20 N. B. What acceleration occurs if the friction force is 4 N?

A. 10 N/kg B. 8 N/kg

Free fall is motion in which gravity is the only force acting. A. Is a skydiver who has reached terminal speed in free fall? B. Is a satellite circling Earth above the atmosphere in free fall?

A. no b/c air resistance B. yes - no opposing frictional forces

What is the acceleration of an object that moves at constant velocity? What is the net force on the object in this case?

Acceleration = 0 Net force = 0

In terms of impulse and momentum, why do airbags in cars reduce the chances of injury in accident?

Air bags increase the time the force is applied and decrease the force, so the result is a lesser force for a longer duration and less damage will occur.

Why is it a good idea to have your hand extended forward when you are getting ready to catch a fast-moving baseball with your bare hand?

An extended hand can move a greater distance when the ball is caught. The greater the distance is accompanied by a longer time, which results in less force.

Why can atoms not be seen with a powerful optical microscope?

Atoms cannot be seen with a powerful optical microscope because they are much smaller than a wavelength of light in the optical microscope. An electron beam needs to be used because the atom is larger than the tiny wavelengths.

The atoms that constitute your body are mostly empty space, and structures such as the chair you're sitting on are composed of atoms that are also mostly empty space. So why don't you fall through the chair?

Because of the electrical force of repulsion

Which of the following are pure elements: H2, H2O, He, Na, NaCl, H2SO4, U?

H2, He, Na, U

A particular atom contains 29 electrons, 34 neutrons, and 29 protons. What is the identity of this element and its atomic number?

Identity = Copper Atomic Number = 29

When vertically falling sand lands in a horizontally moving cart, the cart slows. Ignore any friction between the cart and the tracks. Give two reasons for this, one in terms of a horizontal force acting on the cart and one in terms of momentum conservation.

In terms of force: When the sand lands on the cart it is brought up to the cart's speed. This means a horizontal force provided by the cart acts on the sand. By action-reaction, the sand exerts a force on the cart in the opposite direction, which slows the cart. In terms of momentum conservation: since no external force act in the horizontal direction, the momentum after the car catches sand equals the momentum before. Since mass is added, velocity must decrease.

atoms of the same element that have different numbers of neutrons are known as

Isotopes

What does the atomic number of an element tell you about the element?

It identifies an element bu telling the number of protons in the nucleus.

A fully dressed person is at rest in the middle of a pond on perfectly frictionless ice and must get to shore. How can this be accomplished? Explain in terms of momentum conservation.

Momentum is conserved so the person needs to take off some clothing and throw it in the opposite direction to which he needs to go. The person has no momentum to start off with, so after he's thrown his clothing, the total momentum of person and clothing must be zero. For every action there is an equal and opposite reaction; but this is still true of the person's momentum is non-zero provided it has the same magnitude and opposite direction as the clothing's momentum. Lastly, since there is no friction there will be an equal and opposite force on them that causes them to slide all the way to the shore.

When a cannonball is fired, momentum is conserved for the system of cannon + cannonball. Would momentum be conserved for the system if momentum were not a vector quantity? Explain

Momentum would not be conserved if force is exerted, and therefore impulse is not a vector quantity.

What does EF=0 mean?

Net force = 0 and mechanical equilibrium

A bowling ball sits at rest. Another ball rolls down a lane at constant speed. Which, if either, is in equilibrium?

Only the ball at rest because there is no change. The ball rolling at at a constant speed could be changing direction because it is not rolling at constant velocity.

How does the weight of a falling body compare with the air resistance it encounters just before it reaches terminal velocity? Just after it reaches terminal velocity?

Right before: air resistance is less than weight Just after: air resistance = weight (terminal velocity)

Why does a heavy parachutist fall faster than a lighter parachutist who wears a parachute of the same size?

Same size chute means air resistance acts differently. The heavier has greater terminal speed; he must fall faster and longer, for air resistance against the chute to match his greater weight-- continues to accelerate at greater speeds after the lighter has stopped/reached terminal speed.

Why is it that a cat that falls from the top of a 50-story building will hit a safety net below no faster than if it fell from the twentieth story?

Same terminal speed by both distances

In a periodic table while moving across the period

Size of an atom decreases due to the electrical force of attraction between nucleus and electrons

Which of the following is not a vector quantity?

Speed

Your friend says that the law of momentum conservation is violated when a ball rolls down a hill and gains momentum. What do you say?

The Law of Momentum Conservation states that if no external forces act on a system, then the system's momentum will not change. If you treat the ball as your system, it is clear that the gravitational force is acting on the ball, and provides an impulse, therefore changes the ball's momentum. But this is not a violation of the Conservation of Momentum because there is an external force acting.

In a movie, the hero jumps straight down from a bridge onto a small boat that continues to move with no change in velocity. What physics is being violated here?

The added mass of the man should have decreased the velocity of the boat. If the boat had no change in velocity after the man jumped in, the law of conservation of momentum was violated.

If a ball is projected upward from the ground with 10 kg m/s momentum, what is the momentum of recoil of the world? Why do we not feel this?

The change of momentum of the Earth will be equal and opposite: 10 kg m/s. The Earth is huge, so this change in momentum will produce and incredibly tiny change in the speed of the Earth. It has so much mass that it would have very tiny change to velocity.

Why is a massive cleaver more effective for chopping vegetables than an equally sharp knife?

The cleaver has a greater mass and inertia

If you push horizontally on a crate and it slides across the floor, slightly gaining speed, how does friction acting on the crate compare with your push?

The force of the push is greater than the friction because it's accelerating.

Why doesn't a heavy object accelerate more than a light object when both are freely falling?

The greater mass offsets the equally greater force; force accelerates things, mass resists acceleration --> a = F/m = 2F/2m

If you throw a raw egg against a wall, you'll break it, but if you throw it with the same speed into a sagging sheet it won't break. Why?

The impact time when the egg strikes a sagging sheet is long, so the impact force is small.

A rocket becomes progressively easier to accelerate as it travels through space. Why is this so?

The mass decreases because the rocket burns up fuel as it goes

A lunar vehicle is tested on earth at a speed of 10 km/h. When it travels as fast on the moon, is its momentum more, less, or the same?

The same: p = mv and mass does not depend upon where you are.

Automobiles were previously manufactured to be as rigid as possible, whereas today's autos are designed to crumple upon impact. Why?

The time of the collision is extended so less force must act on the car to slow it to a stop, which is better for the impact on passengers.

The synthesis of a large collection of information that contains well-tested and verified hypothesis about certain aspects of the world is known as scientific

Theory

When you weigh yourself, how does the support force of the scale acting on you compare with the gravitational force between you and Earth?

They are *equal in magnitude and *opposite in direction

If a Mack truck and motorcycle have a head-on collision, upon which vehicle is the impact force greater? Which vehicle undergoes the greater change in its motion? Explain your answers.

They are impacted at the same force. The motorcycle undergoes the greater change in motion because the inertia of the Mack truck is greater.

What occurs when a particle of matter and a particle of antimatter meet?

They transform into radiant energy; annihilate each other.

Where did the heaviest elements originate?

When huge stars imploded and exploded in supernovas.

When is energy most evident?

When it is being transferred, transformed, changed in anyway.

When a ball rolls down an included plane, it gains speed because of gravity. When rolling up, it loses speed because of gravity. Why doesn't gravity play a roll when it rolls on a horizontal surface?

When rolling down, it is going with gravity. Going up, against. When moving horizontally, gravity is perpendicular, neither speeding nor slowing the ball.

An empty jug of weight 'W' rests on a table. What is the support force exerted on the jug by the table? What is the support force when water of weight 'w' is poured into the jug?

Without water the support force is W. With water, the support force is W + w.

Suppose you push to the right on a heavy crate, but not hard enough to make it slide. Does a friction force act on the crate?

Yes, a friction force harder than the force applied.

While standing at rest on a floor, does the floor exert an upward force against your feet? How much force does it exert? Why are you not moved upward by this force?

Yes, a support force equal. The net force = 0 The upward force is not enough to move you upward

A hockey puck slides across the ice at a constant velocity. Is it in mechanical equilibrium? Why or why not?

Yes, it doesn't change its state of motion (accelerate). Some friction does act so it is close to being in equilibrium.

What is the acceleration of a falling object that has reached its terminal velocity?

a = 0

When a care rounds a curve, it is

accelerating

In a periodic table the 18th group of elements

are known as inert gases

When you stand at rest on a pair of bathroom scales, the readings on the scales will always

ass to equal your weight

An object in mechanical equilibrium is an object

at rest AND moving with constant velocity AND having no acceleration

Constant speed in the same direction is

constant velocity

The two measurements necessary for calculating average speed are

distance and time

The chemical properties of matter come mostly from its

electrons

The scientific method is a method for

gaining new knowledge

The most abundant element in the universe is

hydrogen

In science, an educated guess is called a

hypothesis

In each second of fall, the distance of freely falling objects will fall is

increasing

The kind of speed you read on a speedometer is

instantaneous speed

A kilogram is a measure of an object's

mass

If two protons are added to an oxygen nucleus, the result is

neon

Atoms heavier than hydrogen were made by

nuclear fusion

Solid matter is mostly empty space. The reason solids don't fall through one another is because

of electrical forces

In an electrically neutral atom, the number of protons in the nucleus us balanced by an equal number of

orbital electrons

What is known about atoms is that they are

perpetually moving AND recycling among innumerable forms AND *smaller* than the wavelengths of visible light

Of the sciences known as physics, chemistry, and biology, the most basic is

physics

The weight of matter comes mostly from its

protons

The smallest particle of those listed below is

quark

Sciene and technology are

related to one another, but not the same thing

A body undergoes acceleration whenever there is a change in its

speed AND velocity AND direction

Your weight is

the force of gravitational attraction between you and the Earth

When your car moves along the highway at a constant velocity, the net force on it is zero. Why, then, do you continue running your engine?

the friction force and engine force are working in opposite directions. If the engine turned off, the friction force and net force anymore and the car would stop.

What mades an element distinct?

the number of protons

An object weighs 30 N on Earth. A second object weighs 30 N on the Moon. Which has the greater mass?

the one on the Moon

Compared to the atoms that make up the body of an elderly person, the atoms that make up the body of a newborn baby are

the same age

The density of 5 kilograms of iron is

the same as the density of 10 kg of iron

How many different elements are in water (H20) molecule?

two

Which direction does a table push a book resting on it?

up

The equilibrium rule, EF=0, applies to

vector quantities

While an object near the Earth's surface is in free fall, its

velocity increases

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

zero

A hockey puck is set in motion across a frozen pond. If ice friction and air resistance are neglected, the force required to keep the puck sliding at constant velocity is

zero