Mechanics

Question 1

What is a vector quantity?

Answer 1

a physical quantity with direction AND magnitude

Question 2

What are some examples of vector quantities? (5)

Answer 2

force
acceleration
displacement
momentum
velocity

Question 3

What is a scalar quanitity?

Answer 3

a physical quantity that is NOT directional and has a magnitude ONLY

Question 4

What are some examples of scalar quantities? (5)

Answer 4

distance
speed
mass
temperature
energy

Question 5

What is displacement?

Answer 5

a vector quantity- describes how far an object is from where it started and in what direction

Question 6

How can we combine vectors?

Answer 6

-use Pythagoras’ theorem (for two vectors acting at right angles to each other)

-use a scale drawing, find angles using a protractor and use the sine/cosine equation (for vectors not at right angles)

Question 7

What do we mean by coplanar forces?

Answer 7

forces which act in the same plane

Question 8

How can we resolve vectors? Give the equations to find out the Fx and Fy vectors

Answer 8

use trigonometry
-for the horizontal component, Fx = F cos θ
-for the vertical component, Fy = F sin θ

Question 9

How are vectors resolved on a slope?

Answer 9

usually need to resolve weight:
- W cos (θ) perpendicular to the slope
- W sin (θ) parallel to the slope

Question 10

What does it mean if an object is at equilibrium?

Answer 10

-at rest
-no resultant force
-constant velocity

Question 11

What does it mean if a vector triangle is closed?

Answer 11

the forces are at equilibrium

Question 12

What is a moment?

Answer 12

the force multiplied by the perpendicular distance from the line of action of the force to the pivot

Question 13

What is the equation to calculate the moment of a force? Include units

Answer 13

M=Fd

where:
M= moment (Nm)
F= force (N)
d= perpendicular distance from the line of action from the force to the pivot (m)

Question 14

What do the principle of moments state?

Answer 14

at EQULIBIRBIUM, the sum of the clockwise moments= the sum of the anti-clockwise moments ABOUT A GIVEN POINT

Question 15

What do we mean by the centre of mass?

Answer 15

the point at which the entire WEIGHT of an object can be considered to ACT THROUGH

Question 16

What is a couple?

Answer 16

a pair of forces of equal magnitude acting antiparallel either side of a pivot

Question 17

What mnemonic is used for the equations of motion?

Answer 17

SUVAT

where
s= displacement (m)
u= initial velocity (ms^-1)
v= final velocity (ms^-1)
a= acceleration (ms^-2)
t= time (s)

Question 18

How can we work out acceleration if we have 2 velocity’s and 2 times?

Answer 18

-same as a gradient of a velocity-time graph
change in velocity/ change in time

Question 19

How can we work out velocity if we have two displacements and two times?

Answer 19

-same as a gradient of a displacement-time graph
change in displacement/ change in time

Question 20

What doe we mean by instantaneous velocity?

Answer 20

the velocity of an object at a specific point in time

Question 21

How can we work out the average speed/velocity?

Answer 21

velocity:
total displacement/ total time taken

speed:
total distance/ total time taken

Question 22

What is the gradient of a displacement-time graph at a specific point equal to?

Answer 22

instantaneous velocity

Question 23

What is the gradient of a velocity-time graph equal to?

Answer 23

acceleration

Question 24

What is the area under a velocity-time graph equal to?

Answer 24

overall displacement

Question 25

What is the area under an acceleration-time graph equal to?

Answer 25

overall change in velocity

Question 26

When do we use SUVAT equations?

Answer 26

when the acceleration is uniform and resultant force is constant

Question 27

Name all the SUVAT equations (4)

Answer 27

v= u + at s= 1/2(u + v) x t v^2= u^2 - 2as s= ut + 1/2at^2

Question 28

What is something to know when an object is being projected?

Answer 28

the horizontal and vertical components need to be treated independently

Question 29

What do we mean by time of flight?

Answer 29

how long the projectile is in the air

Question 30

What do we mean by the maximum height?

Answer 30

the height at which the projectile is momentarily at rest

Question 31

What do we mean by the range?

Answer 31

the horizontal distance travelled by the projectile

Question 32

What do you do if a projectile is at an angle and with a velocity acting in that direction?

Answer 32

resolve the vectors

Question 33

How do you work out time of flight?

Answer 33

2 x time taken to reach maximum height

Question 34

How can you find the time taken to reach maximum height?

Answer 34

use the SUVAT equations

Question 35

When working with projectiles, what component is always zero for the x-components?

Answer 35

acceleration

Question 36

When working with projectiles/free fall, what would acceleration be for the y-component?

Answer 36

if up is the +ve: if moving up: 9.81 if moving down: -9.81

Question 37

What are the two types of resistive forces?

Answer 37

-contact friction -fluid friction/drag

Question 38

What increases fluid friction/drag? (3)

Answer 38

-increasing viscosity of fluid -increasing speed of the object relative to the fluid -increasing the cross-sectional area of object pushing through the fluid

Question 39

What is lift?

Answer 39

an upwards force on an object moving through a fluid. It is perpendicular to the fluid flow

Question 40

What is thrust?

Answer 40

direction of motion

Question 41

What is the effect of having/not having air resistance in projectile motion?

Answer 41

no air resistance: range and maximum height is increased compared with air resistance: lower maximum height, smaller range (proj. diagram would have an asymmetrical and lower parabola compared to no air resistance)

Question 42

What is terminal velocity? When does it occur?

Answer 42

the maximum velocity an object can have - occurs when resistive forces balance the driving forces

Question 43

RP3: describe this practical

Answer 43

-aim of the experiment is to calculate the value of the acceleration due to gravity, g -done by measuring the time it takes for a ball-bearing to fall a certain distance. The acceleration is then calculated using an equation of motion

Question 44

RP3: what should the graph be? Write the equation of the line

Answer 44

2h/t= gt +2u where: y = 2h/t (m s-1), velocity x = time m = g(m s–2), acceleration y-intercept = 2u, initial velocity

Question 45

What does Newton's 1st law state?

Answer 45

the velocity of an object will not change unless acted on by a resultant force

Question 46

What does Newton's 2nd law state? Write down the equation with units

Answer 46

the resultant force on an object is equal to its rate of change in momentum F= change in momentum/change in time where: F= resultant force (N) momentum= kgms^-1 time= s

Question 47

What equation can you use from Newton's 2nd law for a constant mass?

Answer 47

F= ma where f= resultant force (N) m= mass (kg) a= acceleration (ms^-2)

Question 48

What equation can you use from Newton's 2nd law for a constant velocity?

Answer 48

F= v(change in mass/ change in time) where: F= resultant force (N) v= velocity (ms^-1) mass= kg time= s

Question 49

What does Newton's third law state?

Answer 49

when one body exerts a force on a second body, the second body simultaneously exerts a force of equal magnitude and opposite direction to the first body

Question 50

How can we calculate momentum?

Answer 50

p= mv where: p= momentum (kgms^-1) m= mass (kg) v= velocity (ms^-1)

Question 51

What is the principle of conservation of momentum?

Answer 51

the total momentum before a collision = the total momentum after a collision provided no external force acts

Question 52

What is impulse?

Answer 52

change in momentum

Question 53

What are the equations to work out impulse? What is its unit?

Answer 53

impulse (Ns) = force x change in time or impulse (Ns) = change in momentum

Question 54

When are the impulse equations used?

Answer 54

when force is constant

Question 55

How can we work out impulse from a force-time graph?

Answer 55

area of the graph

Question 56

What is something to know about energy?

Answer 56

total energy is always conserved

Question 57

What does the principle of the conservation of energy state?

Answer 57

energy cannot be created or destroyed, only be transferred from one store to another

Question 58

What do we mean by an elastic collision?

Answer 58

when there is no loss of kinetic energy in the collision

Question 59

What do we mean by an inelastic collision?

Answer 59

when the colliding objects have less kinetic energy than before

Question 60

What happens to the kinetic energy in an inelastic collision?

Answer 60

some of the energy will be shifted to the surroundings e.g thermal stores

Question 61

What does it mean if objects couple together after a collision?

Answer 61

they must have undergone an inelastic collision

Question 62

What is work?

Answer 62

the amount of energy transferred when an external force causes an object to move over a certain distance

Question 63

How can we calculate the work done?

Answer 63

W=fs where: W= work done (J) f= force (N) s= displacement (m)

Question 64

How can you calculate the work done of the force is at an angle?

Answer 64

W = Fs cos θ (or sin θ)

Question 65

How can you find the work done from a force-displacement graph?

Answer 65

find the area

Question 66

What is power?

Answer 66

the rate of energy transfer

Question 67

How can we calculate power?

Answer 67

Power (W) = change in work done/ change in time

Question 68

How can we calculate power if an object is moving at a constant velocity with a constant force?

Answer 68

P=Fv where P= power (W) F= force (N) v= velocity (ms^-1)

Question 69

What does the force need to be in order to use the P=Fv equation?

Answer 69

must be in the direction of the velocity

Question 70

What is efficiency?

Answer 70

How useful something is/how efficient it is

Question 71

What are the two equations to calculate efficiency?

Answer 71

(useful power output/total power input) x 100 or (useful energy output/total energy input) x 100