Mechanics 1 Flashcards
Definition of a vector
a quantity with both magnitude and direction
3 examples of vectors
displacement
velocity
acceleration
Definition of a scalar
a quantity with magnitude but not direction
how do you represent a vector
draw an arrow
u
initial velocity
v
final velocity
s
displacement
t
time
a
acceleration
definition of displacement
the distance travelled in a particular direction
definition of speed
distance / time
definition of velocity
displacement / time
definition of acceleration
time
what do you have to do if you give a definition in algebraic form
you must explain the notation
distance time graph, at the origin; the initial speed is zero
false
the car passed through the starting point while moving
time interval between consecutive dots on a ticker-tape-timer
0.02 s
how to calculate velocity on a ticker-tape-timer
distance of 6 over 0.02 by 6
what does uniform velocity on a ticker-tape-timer
dots are equal measure apart
why do we use more than one space on a ticker-tape-timer when it is uniform velocity
get an average
why do we use more than one space on a ticker-tape-timer when it is non-uniform velocity
we are supposed to get an average of 5-6 spaces
how to calculate acceleration on a ticker-tape-timer
find velocity
acceleration = v-u over t
what is t when calculating acceleration on a on a ticker-tape-timer
0.02 x amount of dots you used
how does data logging work?
an electromagnetic wave from a sensor reflects offa moving trolley
what can data logging be used to measure
velocity
acceleration
acceleration due to gravity
(-) 9.8 m/s squared
formula used to calculate acceleration due to gravity in the experiment
s= ut + 1/2at squared
2 note on accuracy for measuring acceleration due to gravity experiment
do it 5 times and get an average
avoid error of parallax when measuring with a metre stick
slope of a 2xdistance time squared graph
would give you acceleration (due to gravity)
Newton’s first law
a body continues in a state of rest or uniform motion in a straight line unless a resultant external force acts upon it
according to newton’s first law, what will happen to a stationary object
it will remain at rest forever unless a resultant external force acts on it
according to newton’s first law, what happens to an object moving in a straight line
it will keep travelling in a straight line at constant speed and will do so forever unless a force acts on it
all objects have inertia which is…
refusal to change their state of motion
what is a measure of a body’s inertia
mass
mass is measured in
kg
what is the purpose of seat belts in cars
to overcome the inertia of moving passengers
what does the law of friction usually do
it opposes the motion
1 bad thing that friction causes
the wearing in machines due to moving parts rubbing together
1 way to reduce friction
using oil, lubricants etc.
1 benefit of friction
brakes on cars
definition of friction
a force that opposes the relative motion of two objects in contact
momentum
mass multiplied by velocity
p =
m x v
p
momentum
m
mass
v
velocity
is momentum a vector or a scalar quantity
vector
Newton’s second law
When a resultant external force acts on a body, the rate of change of momentum of the body is proportional to the force and takes place in the direction of the force
Force ∝
the rate of change of momentum
F ∝ (1)
t
F ∝ (2)
(u-v)
—– x m
t
F ∝ (3)
ma
F =
Kma
K, constant for force
1
k=1 so F=
ma
force, vector or scalar
vector quantity
mass 3
a scalar quantity, constant value, unit is kg
weight 3
a vector quantity, variable depending on height above ground, unit is newton
Definition of mass
a measure of a body’s inertia
Definition of weight
the force of gravity acting on a body
Newton’s third law
To every action there is an equal and opposite reaction. Action and reaction do not happen on the same body
if someone is in a lift and F= 0
they experience a feeling of weightlessness in zero gravity
State the law of conservation of momentum
when two or more bodies interact in a closed system, the total momentum of the bodies before the interaction equals the total momentum of the bodies after the interaction
conservation of momentum equation
m1u1 + m2u2 = m1v1 + m2v2
Definition of work
force multiplied by displacement
W =
F x s
W
work
F
force
s
displacement
is work a vector or scalar
scalar
unit of work
J
joule
1J =
1N x 1m
Definition of energy
the ability to do work
unit of energy
J
joule
Conservation of energy
Energy cannot be created or destroyed but may be changed from one form to another
Definition of kinetic energy
the energy an object has due to its motion
Ek =
1/2 m v squared
Definition of potential energy
the energy an object has due to its position, shape or state
E p =
m g h
Definition of power
the rate at which work is done
unit of power
W watt
P =
W/t
power =
work over time
1W =
1J /1s
percentage efficiency =
Po/Pi
Po
power output
Pi
power input
electricity is used to rotate an electric motor
electrical to kinetic
the food we eat is used to give to energy to move
chemical to kinetic
electricity is used to power a speaker in a music system
electrical to sound
electricity is used to recharge a battery in a phone
electrical to chemical
renewable sources of energy
forms of energy that will not be used up
2 examples of renewable energy
hydroelectricity
solar energy
what is hydroelectricity
converting the kinetic energy of flowing water into electricity
what is solar energy
using the suns energy to heat water (solar panel) or to generate electricity (solar cell)
non-renewable sources of energy
forms of energy that will not be used up
4 non-renewable sources of energy
oil
gas
turf
coal
how does the sun get it energy
mass is converted to energy in a process called nuclear fusion
What is the resultant force when 12 N east is added to 7.5 N west?
n
What is the resultant when a horizontal force of 12 N is added to a vertical force of 5 N
h
What is the resultant force when 6 N east, 6 N south and 6 N north west are added?
h
A boat is moving with a velocity of 15 m/s in a direction of 42º north of east. Calculate the components of this velocity heading north and heading east.
h
A river flows at 5m/s south. A boat has a speed of 7m/s. The river is 300m wide. 1. If the boat leaves the bank and heads straight across, what direction will it go and how long will it take to get there?
2. if the boat leaves a point and wants to arrive directly across from that point, what direction will it travel and how long will it take to get to the other side?
n
An object of weight of 900N lies on a surface inclined at 10º above the horizontal, find the component weight acting along the inclined surface
j
a pendulum bob is displaced to one side so that the string makes an angle of 15º to the vertical. The weight of the bob is 12 N. Calculate the component of this weight that causes the bob to move
h
An object starting from rest reaches a speed of 20 m/s in 4 seconds. Calculate the acceleration and the distance travelled.
h
A car started from rest reaches a speed of 12 m/s in 3 seconds. It then travels at this speed for 10 seconds. find the total distance traveled
f
When the brakes are applied to a train it takes 2 minutes to stop while moving a distance of 2 km. If the deceleration was constant, find the initial speed.
e
a car passes a point “A” travelling at a uniform speed of 36 m/s along a straight road. A second car initially at rest leaves “A” 7 seconds later. This car accelerates at 2 m/s along the same straight road. Calculate the time it takes the second car to catch up on the first car.
j
A man rows a boar downstream from “p” to “d” in a time of 40 minutes
- calculate the average speed while moving from “p” to “d”
- Calculate the average speed while moving from “d” to “p”
- calculate the average speed for the return journey (up and back)
jkl
a car travels at 24 m/s for 5 seconds. the brakes are then applied and the car comes to rest in a further 10 seconds. Draw a velocity-time graph of this information and use the graph to calculate the total distance travelled.
j
A car travels at 10 m/s having accelerated from rest for 4 seconds. It maintains this speed for 1 minute. It then takes 2 seconds to stop the car. Draw a velocity-time graph of this information and use the graph to calculate the total distance the car travelled.
g
A car starts from rest and accelerates at 4 m/s^2 for 5 seconds. It then travels at a uniform speed for the next 12 seconds. It then decelerates to rest in a further 8 seconds. Draw a velocity-time graph of this information and use the graph to find the total distance travelled and the average speed for the entire journey.
l
A sprinter can start with a velocity of 6m/s. He then runs with a uniform acceleration. Using a velocity - time graph calculate the greatest velocity reached if he can run 100m in a time of 10 seconds.
b
An object is thrown vertically upwards at a speed of 30 m/s
1. calculate the maximum height reached
2. the speed when it is half way up to the maximum height
3. the time to reach half this maximum height
4. the times when its height is 40m
(let g=9.8 m/s^2)
g
An object falls from rest at a height of 200m above ground level. What is the height of the object after 5 seconds ? (let g=9.8 m/s^2)
h
A small ball is thrown vertically upwards with a speed of 30 m/s from the roof of a building which is 20 metres high.
calculate:
1. the time to reach the maximum height
2. the total time it takes for the ball to reach the ground
(let g=9.8 m/s^2)
t
An object is thrown vertically upwards. Its speed is 32m/s when it has reached half its maximum height. Calculate:
1. the value of maximum height
2. the speed of the object 1 second after it was initially thrown upwards
3. the average speed for the first half second
(let g=9.8 m/s^2)
h
Calculate the momentum of a 240 gram object moving at 45 m/s north
k
Calculate the weight of 900 grams (let g=9.8 m/s^2)
s
A bullet of mass 12 grams enters a piece of wood travelling at a speed of 500 m/s . It exits from the piece of wood at a speed of 190 m/s. Calculate the average force exerted by the wood on the bullet if the thickness of the wood is 5cm.
h
A person of mass 55 kg stands on a weighing scales on the floor of a lift. The weighing scales is calibrated in newtons. Calculate the reading on the scales when
- the lift is stationary
- the lift moves upwards with a uniform speed of 3 m/s
- the lift accelerates upwards at 3 m/s squared
- the lift accelerates downwards at 3 m/s squared
- the support cable snaps and the lift falls freely under gravity
b
An object of mass 8 kg moves at a speed of 3 m/s to the right. It collides with a second object of mass 6 kg moving at 7 m/s to the left. As a result of the collision the speed of the second object us reduced by 5 m/s. Calculate the velocity of the first object after the collision.
l
A stationary spacecraft of mass 600kg expels 5kg of exhaust gases at a speed of 120 m/s. Calculate the recoil speed of the spacecraft.
k
A sphere “A” of mass m rolls along a frictionless plane with a speed of 0.4 m/s. It collides with a sphere “B” of mass 2m which is at rest. After the collision the spheres move in the same direction as shown. The initial speed of sphere “A” is 0.1 m/s. Calculate the speed of B after the collision.
c
A body of mass 80 grams and travelling with a speed of 5 m/s collides with another body if mass 200g at rest . The bodies coalesce on impact. Calculate
- The change of momentum for each body
- The average magnitude of the force exerted by each body on the other if the change of momentum occurs in 0.1s
h
Calculate the work done to stop a 50kg object moving at 100 m/s in a time of 15 seconds
j
A man carries a 40kg object up 60 steps each of vertical height 25cm. Calculate
- The work the man does on the object
- The gain in potential of the object
- The average power if this happens in a time of 5 seconds
p
A pendulum bob of mass 1.5kg is displaced to one side through an angle of 60º with the downward vertical. The length of a pendulum is 3m. The bob is released and swings downwards. As the bob through the lowest point of its swing. Calculate
- The speed of the bob
- The kinetic energy of the bob
d
An electric motor has a power input of 90 W. It can lift 100kg through a height of 5m in a time of 1 minute and 10 seconds. Calculate the percentage efficiency of the motor.
x
