Mechanics

Question 1

Simple formula for speed?

Answer 1

Speed = distance / time

Question 2

How to convert from ms^-1 to kmph?

Answer 2

Divide by 1000, multiply by 60 *60

Question 3

How to convert from kmph to ms^-1?

Answer 3

Times by 1000, divide by 60*60

Question 4

Equation for v, u, a and t?

Answer 4

V = u + at

Question 5

Equation for s, u, a and t?

Answer 5

S = ut + 1/2 at^2

Question 6

Equation for s, v, a and t?

Answer 6

S = vt - 1/2 at^2

Question 7

Formula for v, u, a, and s?

Answer 7

V^2 = u^2 + 2as

Question 8

Formula for s, u, v and t?

Answer 8

S = 1/2 (u + v) t

Question 9

How do you solve problems with constant acceleration?

Answer 9

Use suvat equations

Question 10

How do you solve problems with variable acceleration?

Answer 10

Use differentiation and integration to go between position, velocity and acceleration

Question 11

What is the derivative order for displacement, velocity and acceleration where acc is not constant?

Answer 11

Disp differentiates to velocity and velocity differentiates to acceleration
(S > v > a)
Integrates in reverse order

Question 12

What is area and gradient on a speed time graph?

Answer 12

Area is distance travelled,
Gradient is acceleration

Question 13

Formula for area of a trapezium?

Answer 13

[1/2 (top + base)] * height

Question 14

How do you find displacement on a speed time graph with variable acc?

Answer 14

Still area under graph so integrate formula for velocity

Question 15

Formula for position (r) when body has no acc?

Answer 15

r = orig. position. + v*t

Question 16

Formulas for position when dealing with const acc?

Answer 16

r = ut + 1/2 at^2 + og. r
r = vt - 1/2 at^2 + og. r

Question 17

What are the accelerations of the components of projectiles?

Answer 17

Vertically, a is -9.8, horizontally, a = 0

Question 18

What common quantity connects horizontal and vertical components?

Answer 18

Time

Question 19

What is the first thing to do when solving projectile problems?

Answer 19

Find the speed and direction at A and resolve into horizontal and vertical components

Question 20

How do you find the magnitude of initial speed in projectiles?

Answer 20

Use Pythagoras with horiz and very components

Question 21

How do you find direction of initial speed with projectiles?

Answer 21

Inverse tan vertical over horizontal

Question 22

Modelling assumption of a smooth pulley?

Answer 22

Tension is equal on either side

Question 23

Modelling assumption of a light string?

Answer 23

Tension is the same through the string

Question 24

modelling assumption of inextensible string?

Answer 24

both particles have same acc

Question 25

modeling assumption for particle?

Answer 25

ignore air resistance, ignore spin, ignore dimensions

Question 26

modelling assumption of rod?

Answer 26

rigid so doesn't bend, has no thickness

Question 27

modelling assumptions of rough, smooth, plane?

Answer 27

smooth: no frictional force opp to motion Rough: resistive force against motion equal to 𝜇R plane: just a flat plane, projectiles usually occur across these

Question 28

what does static/at rest mean?

Answer 28

forces are balanced

Question 29

What does on the point of slipping/limiting equilibrium mean?

Answer 29

friction is maximal since object is on threshold of movement so forces exactly equal

Question 30

what does constant speed mean?

Answer 30

the forces acting on a moving object are either balanced or not there since there is no acc

Question 31

what warrants a closed vector triangle?

Answer 31

three forces adding to equilibrium along their vectors

Question 32

in dynamics, what does force equal? (newton II)

Answer 32

force = mass * acceleration

Question 33

how do you solve dynamics problems?

Answer 33

resolve all forces acting on body into horizontal/vertical (or parallel and perp. for slopes) set resultant force equation equal to ma and solve as required

Question 34

what is the resultant force of a component?

Answer 34

the sum of forces acting on an object in that plane of space

Question 35

what is friction?

Answer 35

resistive force that always acts in a direction to oppose motion/potenetial motion

Question 36

if object is static, what is the equation for friction?

Answer 36

Fr ≤ 𝜇R

Question 37

if in limiting equilibrium or in movement (dynamic), what is equation for friction?

Answer 37

Fr = 𝜇R

Question 38

what values can 𝜇 (coefficient of friction take?

Answer 38

any value between 0 and 1 but no higher

Question 39

how do you resolve forces on slopes?

Answer 39

perp. and parallel to the slope

Question 40

for mass on slope, how do you resolve weight?

Answer 40

normal to the slope down: mg Cos x parallel to slope down: mg sin x

Question 41

when will an object move down a slope?

Answer 41

when mg Sin x is less than max friction

Question 42

when will an object remain at rest on a slope?

Answer 42

when frictional force is greater than or equal to mg Sin x if another force has component up slope, object will move up

Question 43

how do you resolve basic force diagrams?

Answer 43

using trig:

Question 44

what does tension/thrust look like on 2 connected particles?

Answer 44

Question 45

How do you deal with resolving forces in lifts?

Answer 45

carefully; separate into sub parts as question requires

Question 46

what must be identified in connected particle diagrams?

Answer 46

friction on each object, tension within the connector, acceleration and direction of acc. positive/negative direction, driving force on one of objects if applicable

Question 47

what must be identified on a connected particle pulley diagram?

Answer 47

weight of connected particles, tension, reaction force on pulley

Question 48

what must be identified on connected particle diagrams across pulley on slope?

Answer 48

particle on slope: - weight along/normal to slope - friction - tension - normal reaction force free particle: - weight - tension pulley: - reaction force on pulley

Question 49

how do you find reaction force on a pulley?

Answer 49

the sum of the tensions on the pulley (T on either side) this should be done trigonometrically if dealing with a slope where T acts in different directions

Question 50

how do you start a connected particle problem?

Answer 50

write f = ma equations of motion for both particles and solve simultaneously for desired quantities

Question 51

how do you treat connected particles after the cable snaps?

Answer 51

as free particles, either moving freely under gravity or if horizontal with no force acting on it (other than friction if required) using this, Suvat can be applied

Question 52

what does uniform mean?

Answer 52

weight acts through symmetrical centre

Question 53

what does non uniform mean?

Answer 53

weight does not act through centre

Question 54

what does at the point of tilting about a mean?

Answer 54

there is no reaction force at support b (see diagram)

Question 55

what forces act on a rod leaning against a wall?

Answer 55

- reaction on floor - reaction on wall - weight vertically down - friction up wall - friction at floor towards wall

Question 56

what forces act on a shelf with suspenders?

Answer 56

- weight down - reaction at wall-shelf join (x force horiz, y force vert) - tension in suspender

Question 57

what forces act on rod resting on floor and peg?

Answer 57

- reaction at peg - weight down - reaction at floor - friction at floor

Question 58

what is a moment?

Answer 58

force * perp distance or perp distance * force

Question 59

what is the principle of moments in equilibrium?

Answer 59

sum of anticlockwise moments = sum of clockeise moments about a point