Motion

Question 1

what is instantaneous speed

Answer 1

it is the speed of the car over a very short interval of time.

Question 2

How do you calculate instantaneous speed

Answer 2

drawing a tangent to the graph and calculate the gradient of the tangent

Question 3

What does this graph imply

Answer 3

A) stationary object
B) constant + speed
C) constant - speed
D) changing speed, slow to fast
E) changing speed, fast to slow
F) constant speed

Question 4

what is the gradient of a distance-time graph?

Answer 4

∆d / ∆t = speed

Question 5

what do displacement-time graphs represent

Answer 5

the gradient represents the velocity of an object.

Question 6

what is the definition of velocity

Answer 6

it is the rate of change of displacement per unit time

Question 7

What is the definition of speed

Answer 7

it is the rate of change of distance per unit time

Question 8

what is the formula and units for acceleration

Answer 8

a = ∆v / ∆t units: ms^-2

Question 9

What is the gradient of a velocity-time graph?

Answer 9

∆v / ∆t = a

Question 10

what do these velocity-time graphs represent

Answer 10

Question 11

What does the AREA of a velocity-time graph represent?

Answer 11

ms^-1 x s = m

from v x t = s

Question 12

define stopping distance

Answer 12

it is the total distance travelled from when the driver first sees a reason to stop, to when the vehicle stops

Question 13

what are the two components of stopping distance

Answer 13

thinking distance + braking distance = stopping distance

Question 14

define thinking distance

Answer 14

the distance travelled between the moment when you first see a reason to stop, to the moment when you use the brake.

Question 15

define braking distance

Answer 15

the distance travelled from the time the brake is applied until the vehicle stops

Question 16

what is the formula for thinking distance?

Answer 16

thinking distance = speed x reaction time

Question 17

when is an object said to be in free fall?

Answer 17

when an object is accelerating under gravity, with no other force acting on it

Question 18

what is implied when an object is thrown

Answer 18

• the vertical velocity changes due to gravity
• horizontal velocity remains constant

Question 19

why does the horizontal velocity of the projectile remain constant

Answer 19

the acceleration of free fall is vertically downwards, the component of this acceleration in the horizontal direction is 0

Question 20

how can we calculate the actual velocity of a projectile

Answer 20

Question 21

when an object is fired at an angle θ how can the motion be analysed

Answer 21

splitting the force into components

v_x= v(cos(θ))

v_y= v(sin(θ))

Question 22

how can we use an electromagnet and trapdoor to calculate g

Answer 22

• an electromagnet holds a small steel ball above a trapdoor
• when current is switched off, a timer is triggered,
• the ball falls
• when it hits the trapdoor, the electrical contact is broken and the timer stops.
  
  • calculate g from height and time taken

Question 23

example of electromagnet and trapdoor practical

Answer 23

Question 24

how can we use Light Gates to calculate g

Answer 24

• two light beams, one above the other, with detectors connected to a timer
• when the ball falls through the first beam, it interrupts light and timer starts
  
  • when the ball falls through the second a known distance the timer stops

Question 25

how can we use **pictures** to calculate **g**

Answer 25

* a steel ball is dropped from test next to a metre rule, its fall is recorded on video * the position of the ball at regular intervals is then determined by examine the recording

Question 26

example of using **pictures** to calculate **g**

Answer 26

Question 27

define weight

Answer 27

the gravitational force acting on an object through its centre of mass

Question 28

define drag

Answer 28

frictional force that opposes the motion of the object in fluid * speed ∝ drag² * increased cross sectional area increases drag

Question 29

define upthrust

Answer 29

an upward buoyancy force acting on an object when it is in a liquid

Question 30

representing an object on a slope

Answer 30

Question 31

terminal velocity

Answer 31

when the drag force on an object is equal and opposite to the weight of the object, there is no resultant force and therefore the speed remains constant

Question 32

define moment

Answer 32

the moment of a force is the turning effect of a force about some axis or point * moment = force x perpendicular distance of the line of action of the force or point of rotation * moment = Fx

Question 33

principle of moments

Answer 33

for a body in rotational equilibrium, the sum of the anticlockwise moments is equal to the sum of clockwise moments about the same point

Question 34

define couple

Answer 34

two forces must be parallel and along different lines in the opposite direction

Question 35

define torque

Answer 35

the moment of a couple is known as a toque it is defined as * torque of a couple = one of the forces x perpendicular separation between the forces = Fd

Question 36

define pressure

Answer 36

the normal force exerted per unit cross-sectional area * p = F/A * calculate pressure in liquids * p(ressure) = hpg * h - height of the liquid column * p - density * g - gravity

Question 37

archimedes principle

Answer 37

the upthrust exerted on a body immersed in a fluid whether fully or partially submerged is equal to the weight of the fluid that the body displaces

Question 38

upthrust formula

Answer 38

upthrust = Axpg A - area x - depth p - density g - gravity

Question 39

what is work done

Answer 39

work done = force x distance moved in the direction of the force W = Fx

Question 40

principle of conservation of energy

Answer 40

the total energy of a closed system remains constant: energy can never be created or destroyed, but it can be transferred from one form to another

Question 41

energy exchange

Answer 41

E_k = ½mv² GPE E_p = mgh mgh = ½mv² gh = ½v²

Question 42

define power

Answer 42

power is the rate of work done p = w/t p- power w - work done t - time

Question 43

power and motion

Answer 43

* a constant force F moves the car a distance x in a time t * work done by the force W = Fx * P= w/t = Fx/t * (x/t) = velocity * P = Fv

Question 44

efficiency formula

Answer 44

efficiency = ( useful output energy / total output energy ) x 100

Question 45

tensile and compressive forces

Answer 45

* forces that produce extension are known as tensile forces * forces that shorten an object are known as compressive forces * a helical spring undergoes tensile deformation when tensile forces are exerted * similarly compressive deformation occurs when compressive forces are exerted

Question 46

hookes law

Answer 46

* the extension of the spring is directly proportional to the force applied as long as the elastic limit of the spring is not exceeded * F = kx * k - force constant which is a measure of the stiffness of a spring

Question 47

describe the force extension graph

Answer 47

* straight line from the origina up to the elastic limit (A) * in this region it undergoes elastic deformation, will therefore return to its original length when the force is removed * beyond A is plastic deformation: permanent structural changes to the spring occur and doesnt return to its original state * area under graph = work done

Question 48

elastic potential energy

Answer 48

E = ½Fx = ½(kx) \* x F - force producing an extension x E = ½kx²

Question 49

tensile stress

Answer 49

* defined as the force applied per unit cross-sectional area of the wire * tensile stress = force/cross-sectional area * *σ = F/A*

Question 50

tensile strain

Answer 50

defined as the fractional change in the original length of the wire tensile strain = extension/original length Ɛ = x/L

Question 51

Answer 51

* stress ∝ strain from the origin to P, the limit of proportionality * E represents the elastic limit * elastic deformation occurs up to the elastic limit and plastic deformation beyond that * y1 and y2 are upper and lower yield points ,where material extends rapidly * UTS , ultimate tensile strength is the maximum stress that a material can withstand when being stretched before it breaks

Question 52

young modulus

Answer 52

the ratio of stress to strain for a particular material is a constant and is known as its young modulus, E. young modulus = tensile stress/ tensile strain E = *σ / Ɛ*

Question 53

newtons first law

Answer 53

an object will remain at rest or continue to move with constant velocity unless acted upon by a resultant force.

Question 54

newtons third law of motion

Answer 54

when two objects interact, they exert equal and opposite forces on each other

Question 55

momentum

Answer 55

product of mass and velocity p = mv

Question 56

principle of conservation of momentum

Answer 56

for a system of interacting objects, the total momentum in a specified direction remains constant, as long as no external forces act on the system

Question 57

what is the difference between perfectly elastic and inelastic collisions

Answer 57

Question 58

newtons second law

Answer 58

the net force acting on an object is directly proportional to the rate of change of its momentum and is in the same direction F = P/t F is the net force, P is the change in momentum over time interval t

Question 59

F = ma for momentum

Answer 59

* F = ma * a = (v-u)/t * F = m(v-u)/t * F = (mv-mu)/t * F = p/t