M3 Newton's Laws and Momentum Flashcards by Emma Barker

how are acceleration and force related

acceleration is directly proportional to force

the bigger the force, the greater the acceleration

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how do we represent force

use an arrow
the direction of the arrow shows the direction of the net force
the size of the arrow shows the magnitude of the force

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define newton

the force that will give a 1kg mass an acceleration of 1 ms^-2

units = kgms^-2

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what’s the equation for weight

mass X gravitational field strength

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for objects of different masses what do they have the same?

acceleration

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what is the difference between mass and weight

mass is the same everywhere

weight depends on the gravitational field strength

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would a moon buggy be easier to push on the moon? would it be easier to lift?

pushing it would be the same because the mass and acceleration are the same and F = ma so the force would be the same regardless of where you were

lifting would be easier of the moon because g is smaller on the moon and W = mg so the weight would be smaller hence being easier to lift

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draw a velocity-time graph for someone in free fall

increases, reaches terminal velocity, parachute released, decreases, terminal velocity again

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What does the magnitude of drag depend on

Speed of object
Cross sectional area of object
Roughness or texture of object
Density of fluid the object is travelling through

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What is the special theory of relativity

As you approach the speed of light, mass is no longer constant
So F=ma doesn’t apply

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Define work

Force applied X distance moved in the direction of the force

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Define joule

The energy transferred when a force of 1N is applied over a distance of 1m

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What is the equation for work done when there’s an angle and when there isn’t an angle

When there’s an angle W = Fcos(x)s

No angle W = Fs

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Is work done a scalar or vector

What are its units

Scalar

J or Nm

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Derive the equation for kinetic energy

Ek = Fs

F = ma and s = 0.5(u+v)t and a = (v-u)/t

So Ek = m((v-u)/t) X 0.5(u+v)t
= 0.5m(v-u)(v+u)
=0.5m(v^2 - u^2)
But at the initial velocity there is no kinetic energy so it doesn't need to be there so
Ek=0.5mv^2

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What is the conservation of energy

Energy cannot be created or destroyed

It can be transferred from one form to another, however the total energy will remain constant (in a closed system)

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Derive the equation for gravitational potential energy

Ep = Fs
S is the height
F = mg

Ep = mgh

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what is the elastic potential energy of something

work done by the deforming force

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derive an equation for elastic potential energy

PE = average force X extension
Hooke’s law: F = kx
Average force = 0.5kx

PE = 0.5kx X x
= 0.5kx^2

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in a free fall with no air resistance what happens to the kinetic energy and the potential energy at the start and end

START
Ek = 0
E = Ep + Ek
= mgh + 0

END
Ep = 0
Ek = 0.5mv^2
apply v^2 = u^2 + 2as
u = 0
v^2 = 2as
Ek = 0.5m(2as)
=0.5m(2ah)
a=g
Ek = 0.5m(2gh) = mgh

so Ep at start = Ek at end

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what is the equation for
Ep?
Ek?

Ep = mgh
Ek = 0.5mv^2

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A pendulum has a mass of 5kg and is held at a height of 0.15m
how fast will it move at its lowest point

GPE loss = mgh = 5 X 9.81 X 0.15 = 7.36J
At the bottom the energy is transferred to kinetic energy so
Ek = 7.36 = 0.5mv^2
0.5 X 5X v^2 = 7.36
v = 1.7ms^-1

mgh = 0.5mv^2
gh = 0.5v^2
v = square root of 2gh
= square root of 2 X 9.81 X 0.15
= 1.7 ms^-1

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if there is friction what does Ep equal

Ep = Ek + Wf

Wf is friction which is the force X displacement

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define power

the rate at which work is done

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what are the base units of power

Js^-1

are these scalars or vectors: | power, work done and time

all scalars

what is the equation for efficiency in terms of power

power output / power input X 100

what is power when the force and motion are in different directions

P = Fvcosx

what are the equations for kinetic energy

Ek = 0.5mv^2 Ek = mas Ek = Ep - Wf

what do sankey diagrams represent | what are the features of them

represent the efficiency of an appliance useful energy goes to the right and wasted downwards the size of the arrow represents the fraction of energy transformed

what is newton's first law of motion

a body will stay still or move in a straight line at a constant speed unless there is a resultant force acting on it means when there is constant velocity, there is a zero resultant force acting on you

what is Newton's second law of motion

(Resultant) force is (directly) proportional or equal to the rate of change of momentum F = ma or F = change in p / change in t

define stopping distance | what is the equation

distance travelled in the time between a driver first spotting an obstacle and vehicle coming to a complete stop thinking distance + braking distance

what is the equation for thinking distance in terms of SUVAT

s = ut

define thinking distance | what factors affect it

the distance travelled during the driver's reaction time age, tiredness, alcohol, drugs, illness, speed

define braking distance | what factors affect it

the distance travelled after the brakes are applied until the car comes to rest road condition, tyre condition, speed, brake condition, mass of car

what is the equation for braking distance in terms of SUVAT

s = -(u^2) / 2a acceleration will be negative also as the car will be decelerating so the displacement overall will be positive

derive F = p/t into F = ma

``` change in p = mv - mu F = mv - mu / t F = m(v-u) / t mass is constant so F = m (v-u)/t (v-u)/t = a F = ma ```

what is Newton's third law of motion

When body A exerts a force on body B, body B exerts a force on body A that is equal, opposite in direction and of the same type

how would you describe an object with 300N going to the right and 300N going in the opposite direction

balanced | net force = 0N

how would you describe an object with 400N going to the right and 300N going to the left

unbalanced object will move the right 400-300 = 100 resultant force in 100N to the right

a car which is accelerating then changes forces so 400N goes behind and 300N in front what happens

decelerates 300-400 = -100 resultant force is -100N to the left

define resultant force

sum of all the forces acting on an object, taking relative directions into considerations

what is momentum | what does a higher momentum mean

the stop ability of an object | the more momentum an object has, the harder it is to stop

what does p=mv mean | what are the units for momentum

momentum = mass X velocity kgms^-1

is momentum a vector or scalar quantity

vector

what is the equation for change in momentum

p = mv - mu

how can you relate the equation for momentum and newton's 2nd law

``` F = p / t Ft = p Ft = mv - mu ```

A ball hits a wall at 4ms^-1 and bounces back at 3.5ms^1. the mass of the ball is 2kg, what is the change in momentum?

p = mv - mu p = (2 X 4) - (2 X -3.5) = 8 - - 7 = 15 kgms^-1

what is impulse

the product of the force and the time interval over which the forces act

what is the equation for impulse

F X change in t

relate impulse to Newton's 2nd law

``` F = ma = m(v-u)/t =mv-mu / t Ft = mv - mu Ft = p so impulse = change in momentum ```

on a force-time graph, what represents the impulse

area under the graph

is impulse a vector or scalar quantity

vector

how would you reduce the force in a collision

increase the time seat belts crumple zones

what is the conservation of momentum

total linear momentum of two objects before they collide equals the total linear momentum after the collision

apply the conservation of momentum to an air rifle recoiling

the forward momentum gained by the pellet is equal in magnitude to the backward momentum of the rifle

what is an elastic collision

where momentum is conserved and kinetic energy is conserved | so no energy is dissipated into other forms

what does it mean if a collision is inelastic

some of the kinetic energy is converted into other forms during the collision eg. sound or heat (most collisions are inelastic)

what are the steps for 2D momentum | A2

Step 1: Work out the initial horizontal momentum of ball A. Step 2: Work out the horizontal and vertical components of A after the collision Step 3: Use the horizontal component to work out the horizontal velocity of B after the collision Step 4: Use the vertical component to work out the vertical velocity of B after the collision. Step 5: Use Pythagoras to find the magnitude of the velocity and calculate the angle below the horizontal.

what is the conservation of momentum in terms of 2D momentum (A2)

the horizontal momentum before a collision = the horizontal momentum after a collision the verticle momentum before a collision = the verticle momentum after a collision

describe how forces acting on a parachutist change as he falls

the skydiver leaves the plane and accelerates until the -air resistance and his weight equal - he's traveling at terminal velocity but this is too fast to land - the parachute is opened which increases the air resistance making it larger than weight - he slows down until air resistance equals weight again, reaching terminal velocity again but at a safer level to land

define terminal velocity

this occurs when the frictional forces and the driving force of an object equal

M3 Newton's Laws and Momentum Flashcards

(63 cards)