Chapter 2 Mechanics

Question 1

Newton’s first law of motion

Answer 1

An object continues to remain stationary or to move at a constant velocity unless an external force acts on it.

Question 2

Newton’s second law of motion

Answer 2

F= m x a

Question 3

Newton’s third law of motion

Answer 3

Every action has an equal and opposite reaction. Action-reaction pair must be of the same type.

Question 4

F = 0

Answer 4

equilibrium

Question 5

Block moves

Answer 5

dynamic friction

Question 6

Block remains stationary

Answer 6

static friction (higher than dynamic friction)

Question 7

Dynamic friction

Answer 7

Ff = N (or R) x coefficient of dynamic friction

relative movement, lower thatn maximum static friction

Question 8

Static friction

Answer 8

Ff < or = N (or R) x coefficient of static friction

no relative movement, no motion

Question 9

Net force

Answer 9

Resultant force = vector sum

Question 10

Velocity negative

Answer 10

direction is changed

Question 11

First equation of motion

Answer 11

v = u + at

Question 12

Second equation of motion

Answer 12

s = ut + 1/2 at^2

Question 13

Third equation of motion

Answer 13

v^2 = u^2 + 2as

Question 14

Fourth equation of motion

Answer 14

s = (v+u)/2 x t

Question 15

SUVAT equations

Answer 15

are only appliciable when the acceleration is constant

Question 16

Another form of v = u + at

Answer 16

0 = u - gt

Question 17

Another form of s = ut + 1/2 at^2

Answer 17

h = ut + 1/2 gt^2

Question 18

Another form of v^2 = u^2 + 2as

Answer 18

0 = u^2 - 2gh

Question 19

Horizontal and vertical motions

Answer 19

Two motions, horizaontal and vertical are completly independent of each other.

Question 20

Horizontal speed

Answer 20

cos, continous unchanged

Question 21

Vertical speed

Answer 21

sin, changes as gravity acts on the object

Question 22

Force

Answer 22

N (kgms^-1)

Question 23

Translational equilibrium

Answer 23

object is at rest or moving at constant velocity (straight line) which means that 0 force is acting on the object

Question 24

Three vectors

Answer 24

form a closed triangle = translational equilibrium

Question 25

Coefficient greater than 1 (friction)

Answer 25

the surfaces’ friction is very strong and greater thatn the weight of the object

Question 26

Drag force

Answer 26

holding back, holds back, e.g. through water or air = resistance
Some energy of main body is transfered inot the fluid (water or air) it is moving through. Some fluids absorb this energy better than others. E.g. svimming vs. running.

Question 27

Air resistance

Answer 27

increases as speed increases -> net force and acceleration decreases.

Question 28

Car speed

Answer 28

Speed doubles - drag force increases by four

Question 29

Terminal speed (skydiving)

Answer 29

weight force downwards and resistance force upwards are equal -> cancel out -> no more acceleration -> constant speed.

Question 30

Joule

Answer 30

One joule is the energy required when a force of one N acts through a distance of one meter.

Question 31

Principle conservation of energy

Answer 31

energy cannot be created or destroyed

Question 32

Work (done)

Answer 32

force (N) x distance moved in direction of force (m)
= F cosV x s
Is done when a resistive force is operating too
= force acting x distance traveled x cosV

Question 33

Constant force (on graph)

Answer 33

Straight line or parallel to the x-axis

Question 34

Power

Answer 34

rate of doing work
= energy transferred / time taken for transfer
Js^-1 = W (Watt)
P = W/t = F x (s/t) = F x v

Question 35

Kinetic energy

Answer 35

energy an object has because of its motion (speed increases)
= 1/2 mv^2
= 1/2 m(v^2 - u^2) if moving

Question 36

Potential energy

Answer 36

energy an object has because of its position in a gravitational field
Mass moved vertivally up or down = gains or loses gravitational potential energy
= mgh

Question 37

Energy moving between Ek and Ep

Answer 37

v = (2gh)^1/2

Question 38

Elastic potential energy

Answer 38

stored energy returned (e.g. spring)
Hooke’s law
F = k x
Ep = 1/2 k x^2

Question 39

Efficiency

Answer 39

some energy lost to internal energy or to surroundings (heat)
= usful power out / total power in
= useful work out / total energy in

Question 40

Momentum

Answer 40

p = mv (never speed)
unit kgms^-1
net force leads to change in momentum

Question 41

Collisions

Answer 41

any interaction where momentum transfers
total momentum does not change (because no outside forces are taken into account)
Momentum is always constant is no external force acts on the system.

Question 42

Elastic collision

Answer 42

two objects (same mass), one initially stationary, no energy lost, one finally stationary
m1u = m2v, m1 = m2, u = v
kinetic energy does not change

Question 43

Inelastic collision

Answer 43

two objects (different masses), no energy lost
m1u1 + m2u2 = m1v1 + m2v2
kinetic energy is conserved

Question 44

Total inelastic collision

Answer 44

two objects, no energy lost, keep together after collision

m1u1 = (m1 + m2) x v

Question 45

Explotion

Answer 45

two objects, energy gained, collide in separate directions

m1 / m2 = -v2 / v1

Question 46

Kinetic energy and momentum

Answer 46

Ek = p^2 / 2m

Question 47

Impulse

Answer 47

F x t unit Ns

F x t = change in p (momentum)

Question 48

Helicopter momentum equation

Answer 48

Mg = v (change in momentum / change in time) or

kgs^-1 x ms^-1

Question 49

Rocket momentum equation

Answer 49

a = - (v x change in mass) / (m x change in time)

the negative sign indicates the loss of mass while the gain in speed.