Chapter 4 Momentum and Energy

What happens to the kinetic energy if you double the speed of the car?

its kinetic energy is now increased by four .

If the pivot point or fulcrum of the leveler is relatively close to the load, and you apply a small input force will the output force be large or small?

large. Because the input force is exerted through a large distance and the load is moved over correspondingly short distance.

The longer the force the larger or smaller the momentum?

larger

Impulse?

the quantity force x time interval great force for a long time = large impulse great force for small time = small impulse

what is power?

the rate at which work is done work done/time interval watts

If the boxer makes the time of contact three times longer by riding with the punch, by how much is the force reduced

1/3

What is the chemical reaction for photosynthesis

6CO2 + 6H2O + sunlight = C6H12O6 + 6O2

What happens if momentum changes while the mass remains the same and the velocity changes?

Acceleration occurs

Why do cells need energy?

Cells need energy so that they can do all the things that require work. To move, to change their shape, to reproduce, to maintain and repair cellular structures, or to create new cells.

inelastic collision

Colliding object dont rebound. MOMENTUM IS STILL CONSERVED.

What doesn't change?

ENERGY

does there have to be an internal or external force on an object to change momentum?

EXTERNAL

an automobile going 100km per hour has how much kinetic energy if it were going 50km per hour?

Four times as much kinetic energy.

How do plants obtain glucose? How do animals obtain it?

Plats obtain glucose through photosynthesis animals obtain it by breaking down nutrients in the foods they eat such as proteins carbohydrates and fats.

if the brakes of a bicycle become locked and the bike skids to a stop, how much farther will the bike skid if its moving three times as fast?

It will skid 9 times farther

kinetic energy

Kinetic energy is the energy associated with a moving body by virtue from of its motion alone. KE = 1/2massxspeed^2

does a moving object possess impulse?

NO remember that an object cannot posses force. therefore the object can't possess impulse. It has to interact with another object to have impulse same as force.

can a machine multiply work or energy?

NO!

does an object at rest have momentum?

NO.

What do we say in any collision?

New momentum before collision = net momentum after collision.

can an object posses work?

No unlike energy work is not something an object has. Work is something an object does to another object.

A boxer being hit with a punch tries to extend the time of contact for best results, whereas a karate expert delivers a blow in a short time for best results. Isn't there a contradiction here?

Not there isn't because the best results for each are different. The best result for the boxer is reduced force which is accomplished by maximizing time. The best result for the karate expert is increased force delivered in the shortest possible time.

the momentum of the cannonball is equal to and opposite to the momentum gained by the recoiling cannon, true or false?

TRUE. they cancel.

Talk about work and kinetic energy

The change in kinetic energy is equal to the work done. work = changeKE

What is the ultimate source of the energy that powers most life on earth? Explain.

The sun it is the source of energy plants need to perform photosynthesis.

When do a 1000kg car and a 2000kg truck have the same momentum?

When the 1000kg car is going twice as fast as the truck. because 1000x2 = 2000. If they are both at rest they have the same momentum

rows of wind powered generators are used in various windy locations to generate electric power. Does the power generated affect the speed of the wind? Would locations behind the windmills be windier if the windmills weren't there?

Windmills generate power by taking kinetic energy from the wind, so the wind is slowed by interaction with the windmill blades. SO yes it would be windier behind the windmills if they weren't present.

can a huge ship moving at a slow velocity have the same momentum as a small bullet moving at a high velocity?

YES

Does a moving object posses momentum?

YES. a moving object can possess momentum but like velocity only in a relative sense. That is, with respect to a frame of reference such as earth surface. For example a Fly may have a large momentum if he is moving inside a fast moving airplane BUT has little momentum relative to the cabin.

What is a machine?

a device for multiplying forces or simply changing the direction of forces.

one joule of work is done when?

a force of 1n is exerted over a distance of 1meter in the direction of the force as in lifting an apple over your head.

what is a newton meter?

a joule.

What can you do to produce maximum increase in momentum?

ally the greatest force but also extend the time of application for as long as possible.

Why is a heavier truck harder to push than a lighter truck?

because the heavier truck has a larger momentum.

The greater the impulse exerted on something the greater will be its...

change in momentum Impulse = Change in momentum OR Ft=change in mv.

what does momentum depend on?

depends on velocity

efficiency ?

efficiency = work done / energy used.

Whenever you want the time of contact to be small what should you do?

extended the time of the contact

What is an example of an elastic collision?

gas molecules.

What is the principal energy source by most living things?

glucose

what are some forms of kinetic energy?

heat sound and light.

What do automobiles convert their keltic energy into?

heat.

whenever you exert a force on something you also exert a?

impulse

The law of conservation of momentum

in the absence of an external force the momentum of a system remains unchanged.

The law of conservation of energy

in the absence of external work input or output the energy of a system remains unchanged energy cannot be created or destroyed.

what is momentum

inertia in motion or the product of the mass of an object and its velocity.

talk about work when lifting and holding a barbell

lifting there is work done holding there is not.

Momentum

mass x velocity is inertia in motion

are momentum and kinetic energy the same thing?

momentum is a vector and keltic energy is a scalar

is energy lost or gained when it is transformed or transferred?

neither lost nor gained. THINK THERMALLY

If you toss a ball horizontally while standing on a skateboard you will roll backward with the same amount of momentum that you have given to the ball. Will you roll backward if you go through the motions of tossing the ball but instead holding on to it.

no you will not roll backwards without immediately rolling forward to produce no net rolling. If no net force acts on the ball no net force acts on you/

what does kinetic energy depend on?

square of velocity

What is the source of energy for your body?

sugar glucose C6H12O6

If the boxer instead moves into the punch and shortens the contact time by half by how much is the force increased?

the force is two times greater

two cars are moving on a road one is twice as heavy but they are both moving at the same speed how much kinetic energy do they have?

the heavier car has twice as much kinetic energy This is because kinetic energy depends on mass

what is gravitational potential energy

the potential energy energy due to elevated positions PE=mgh

What is really important when finding momentum?

time. how long the force acts.

The amount of gravitational potential energy possessed by an elevated object is equal to the amount of work done against gravity in lifting it up. true or false?

true

the more power the more acceleration? true or false?

true

is momentum a scalar quantity or a vector quantity

vector quantity

ellastic collision

when a moving billiard ball hits another billiard ball at rest, the first ball comes to rest and the second ball moves with the initial velocity of the first ball. Colliding objects rebound without lasting deformation or the generation of heat. Here momentum is conserved because the momentum of the first ball is transferred to the second. also the objects don't change shape when they hit each other, AND no heat is generated.

what does conserved mean?

when a physical quantity remains unchanged during a process that quantity is said to be conserved. Momentum is conserved.

If you are in a fast moving car that is out of control should you hit the haystack or a concrete wall?

whether you hit the haystack or the wall your momentum is decreased by the same amount. so the impulse requiring you to stop is the same.

work is done in lifting a barbell how much work is done in lifting a twice as heavy barbell the same distance? a.twice as much b.half as much c. the same d.depends on speed

wor = force x distance work = mass x gravity x distance A. it doubles.

Work?

work = force x distance

talk about the work when using a machine

work input = work output force x distance (input) = force x distance (output)

Can an object posses energy?

yes but only in a relative sense. An elevated object may possess PE relative to the ground but no energy relative to a point at the same elevation.

Will a car going 100km per hour skid farther?

yes it will skid four times as far when it breaks as if it were going 50km per hour.