Mechanics

Question 1

define the centre of mass

Answer 1

a point within an object through which all forces are acting (point of balance)

Question 2

if a pivot is placed not at the centre of gravity, what will happen to the system

Answer 2

it will rotate

Question 3

if the force of gravity is acting at the same point where the support force is acting, the system will be in ____

Answer 3

equilibrium

Question 4

how do you add vectors

Answer 4

connect head to tail, and then the resultant is from the tail of the first to the head of the second

Question 5

how can you find change using vectors

Answer 5

subtract the vectors, initial - final. this can be used for example with velocity or momentum

Question 6

how do you subtract a vector

Answer 6

add the vector but change the direction of the second one first

Question 7

what formula shows rotational equilibrium

Answer 7

sum of the torques clockwise = sum of the torques anticlockwise

Question 8

what does τ stand for and what is it measured in

Answer 8

torque [Nm]

Question 9

what does F stand for and what is it measured in

Answer 9

force [N]

Question 10

what does d stand for and what is it measured in

Answer 10

distance [m]

Question 11

what does x stand for in the position of centre of mass formula and what is it measured in

Answer 11

x1 is distance to the first object, x2 is distance to the third object, x3 is distance to the third object etc

Question 12

how do you find the position of the centre of mass

Answer 12

start from a reference point. for each object, multiply the distance it is from the reference point by its mass. add these together for all of the objects. then divide this total by the sum of all the masses

Question 13

if a system is made up of several objects the motion of the centre of mass of this system does not change if the system is _____

Answer 13

isolated

Question 14

If the system is isolated, can individual objects change their velocity while the centre of mass continues to move with the same velocity

Answer 14

yes

Question 15

what can the change in momentum also be called

Answer 15

impulse

Question 16

what does p stand for and what is it measured in

Answer 16

momentum [kgms-1]

Question 17

what does t stand for and what is it measured in

Answer 17

time [s]

Question 18

even if an object in circular motion is moving with a constant speed, it will always be accelerated motion. why?

Answer 18

because its direction is constantly changing

Question 19

what force acts in circular motion only

Answer 19

centripetal force

Question 20

In circular motion, the force of gravity is always ___ ___ everywhere round the circle

Answer 20

the same

Question 21

In circular motion, Fc = F___ + F___

Answer 21

tension, g radial

Question 22

at the bottom of a circle of circular motion, in which direction is the tension force

Answer 22

upwards

Question 23

in which direction does the centripetal force act the whole way round the circle

Answer 23

inwards, towards the centre of the circle

Question 24

what formula can you use to work out the constant speed of an object in circular motion

Answer 24

v = 2πr/T –> 2πr is the distance because thats the circumference of a circle

Question 25

what does Fg stand for and what is it measured in

Answer 25

force of gravity, N

Question 26

what does G stand for

Answer 26

gravitational constant, 6.67 x 10^-11

Question 27

what do the m and M stand for in the universal gravitation formula

Answer 27

m is the mass of the smaller heavenly body, M is the mass of the larger one

Question 28

what does r stand for in the universal gravitation formula

Answer 28

the distance between two heavenly bodies

Question 29

what is the relationship between the force of gravity and r (the distance between two heavenly bodies)

Answer 29

Fg is proportional to 1/r^2

Question 30

for universal gravitation, Fg=?

Answer 30

Fc

Question 31

because Fg = Fc for gravitational motion, what two forumlas can be equated to one another to work out velocity with heavenly bodies

Answer 31

GMm/r^2 = mv^2/r

Question 32

the speed of a satellite is _____ if the mass of a primary body is large

Answer 32

greater

Question 33

speed of a satellite is ____ if the distance to the primary body is large

Answer 33

smaller

Question 34

weight force is also known as

Answer 34

the gravitational force

Question 35

how can you work out gravity using the universal gravitation formula

Answer 35

because weight force is the gravitational force, mg=GMm/r^2 so g = GM/r^2

Question 36

what is the difference between rotational and circular motion

Answer 36

if the centre of motion is within an object it is rotational motion, if the centre of rotation is outside the object, it is circular motion

Question 37

what does ω stand for and what is it measured in

Answer 37

angular velocity, rads-1

Question 38

what does θ stand for and what is it measured in

Answer 38

angular displacement, rad

Question 39

what does α stand for and what is it measured in

Answer 39

angular acceleration, rads-2

Question 40

what does T stand for and what is its value in rotational motion

Answer 40

time to complete one revolution, 2π

Question 41

what can angular velocity also be called

Answer 41

angular frequency

Question 42

what does angular frequency actually show

Answer 42

the number of revolutions an object is making in 1 second

Question 43

angular velocity is _____ if the object rotates through the same angle every second

Answer 43

constant

Question 44

what does second newtons law become in rotational motion

Answer 44

τ = Iα - thats an i btw

Question 45

what does I (i) stand for and what is it measured in

Answer 45

rotational inertia, kgm^2

Question 46

what formula applies to rotational inertia when mass is equally distributed, and what does this mean for the actual inertia

Answer 46

I = mr^2/2, the inertia is lower

Question 47

what formula applies to rotational inertia when mass is concentrated on the rim, and what does this mean for the actual inertia

Answer 47

I = mr^2, inertia is higher

Question 48

what are the formulas for rotational and linear kinetic energy

Answer 48

Ekrot = 1/2 Iω^2, Eklin = 1/2 mv^2

Question 49

what is the formula for gravitational potential energy

Answer 49

Egp = mgh

Question 50

what does L stand for and what is it measured in

Answer 50

angular momentum, kgm^2rads-1

Question 51

what are the formulas for linear and angular momentum

Answer 51

linear p=mv, angular L=Iω

Question 52

what is the condition for conservation of angular momentum

Answer 52

if there is no external torque present, angular momentum is conserved

Question 53

when would you use the L=mvr formula for angular momentum

Answer 53

when working out the angular momentum of a particle

Question 54

define simple harmonic motion

Answer 54

periodic motion where an object is oscillating around an equilibrium position due to restoring force

Question 55

define restoring force in terms of its values at different times in the motion

Answer 55

it is max at the extreme positions and =0 at the equilibrium position

Question 56

in simple harmonic motion, when is velocity at its maximum

Answer 56

at the equilibrium position

Question 57

where is the equilibrium position in simple harmonic motion

Answer 57

the middle

Question 58

In SHM, Egp is max at the extreme and is equal to ?

Answer 58

Ek max at the equilibrium

Question 59

what is the amplitude in SHM

Answer 59

the distance between equilibrium and one extreme

Question 60

In SHM, displacement is proportional to?

Answer 60

the restoring force: y ∝ -F (restoring force is in the opposite direction)

Question 61

on a reference circle, what shows the amplitude of the SHM

Answer 61

the distance between the top and bottom of the circle

Question 62

on a reference circle, what shows the y of the SHM

Answer 62

the vertical distance (component) between the middle line (like the equator?) and the point on the reference circle the motion is at

Question 63

define resonance

Answer 63

when an external force is applied to an oscillating system with the same frequency as the natural frequency of a system, it causes a large increase in amplitude which is called resonance

Question 64

velocity (v), acceleration (a) and displacement (y) can all be modelled for SHM using sine and cosine waves. there are two rows of formulas for these on your formula sheet. You would use the first row of formulas for situations where the motion started from?

Answer 64

equilibrium

Question 65

velocity (v), acceleration (a) and displacement (y) can all be modelled for SHM using sine and cosine waves. there are two rows of formulas for these on your formula sheet. You would use the second row of formulas for situations where the motion started from?

Answer 65

maximum displacement

Question 66

describe what a sine wave looks like

Answer 66

positive - starts at the intersection of the two axis and goes up, negative - starts at the same place but goes down first

Question 67

describe what a cosine wave looks like

Answer 67

positive - starts above the intersection of the two axis, at the level of the displacement, velocity whatever and then goes down and then up, negative - starts at a level below the intersection of the two axis at the value and then goes up first before down

Question 68

the ratio of angles from a phasor diagram for SHM is equal to the ratio of?

Answer 68

times

Question 69

for a spring, the resultant force is a result of?

Answer 69

Fgravity and Felastic

Question 70

is bouncing on a trampoline an example of SHM. Why or why not?

Answer 70

no, because the restoring force has to be present during the entire period of oscillation, and when bouncing on a trampoline, it is only present when your feet are in contact with the trampoline