P10 forces and motion

Question 1

what is acceleration?

Answer 1

the change in velocity over a given time

Question 2

what is decceleration?

Answer 2

when an object slows down (negative acceleration)

Question 3

how do you calculate acceleration from a VELOCITY time graph?

Answer 3

the gradient of the graph

Question 4

what is the initial acceleration of an object falling to the earth?

Answer 4

approximately 9.8m/s2

Question 5

what is the acceleration of a falling object due to?

Answer 5

the force of gravity acting on the object

Question 6

what do air particles cause on a falling object?

Answer 6

an upward force of friction to act on the object called air resistance

Question 7

what is terminal velocity?

Answer 7

when the force of air resistance balances the force of gravity so the object stops accelerating and reaches a constant velocity

Question 8

where does terminal velocity apply?

Answer 8

to any falling object through a fluid

Question 9

what affects the terminal velocity of an object?

Answer 9

the shape of the object affects the amount of air resistance on the object. this affects the terminal velocity

Question 10

what is Newton’s first law of motion?

Answer 10

if the resultant force of a stationary object is 0, it will remain stationary
if the resultant force of a moving object is 0, the object will continue to move with the same velocity

Question 11

what is Newton’s second law of motion?

Answer 11

the acceleration of an object is proportional to the resultant force acting on the object and inversely proportional to the mass of the object
aka - F=ma

Question 12

what are the typical speeds of a car on the motorway and a normal road?

Answer 12

approx. 13 m/s on a typical road
approx. 30 m/s on a motorway

Question 13

what is the typical acceleration of a car travelling from a road to a motorway?

Answer 13

2 m/s2

Question 14

what is another way of describing Newton’s first law?

Answer 14

objects will stay still or continue to move with constant motion unless you apply a resultant force

Question 15

what is inertia?

Answer 15

the tendency for an object to stay at rest or continue in uniform motion (due to Newton’s 1st law)

Question 16

what is inertial mass?

Answer 16

a measure of the difficulty of changing an object’s velocity

Question 17

what is Newton’s third law of motion?

Answer 17

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

Question 18

what do all moving objects have?

Answer 18

momentum

Question 19

what is the value of a stationary object’s momentum?

Answer 19

0

Question 20

what is the conservation of momentum?

Answer 20

in a closed system, the total momentum before an event is equal to the total momentum after the event

Question 21

what is momentum?

Answer 21

the product of an objects mass and velocity

Question 22

what is the unit for momentum?

Answer 22

kg m/s

Question 23

why are rapid changes in momentum dangerous?

Answer 23

they can cause large impact forces be exerted on an object/person, causing an injury

Question 24

what are crash tests used for?

Answer 24

to help car manufacturers design car safety features

Question 25

which two equations can be combined together to calculate the force of an object using its change in momentum?

Answer 25

F = ma a = change in velocity / time to make F = (m x v) / t (this is given in the exam)

Question 26

how can the danger of rapid changes in momentum be reduced?

Answer 26

the overall force acting on the person can be reduced by increasing the time taken for the change in momentum to take place. this is due to the equation F = mv / t where an increase in t reduces the overall force.

Question 27

what are some safety devices which slow down momentum change?

Answer 27

airbags seatbelts helmets crash mat cushioned surfaces

Question 28

what is stopping distance?

Answer 28

the distance from when the driver first sees the obstruction to when the car actually stops

Question 29

what are the two parts of stopping distance?

Answer 29

thinking distance braking distance

Question 30

what is thinking distance?

Answer 30

the distance travelled by the car during the driver's reaction time

Question 31

what is braking distance?

Answer 31

the distance the car travels from when the driver applies the brakes to when it stops

Question 32

what is reaction time?

Answer 32

the time it takes for the driver to spot the obstruction, make a decision and then put their foot to the brake

Question 33

how is the stopping distance affected due to the speed of the car?

Answer 33

the greater the speed, the greater the stopping distance (assuming the same force is being applied to the brakes)

Question 34

what affects reaction time and stopping distance?

Answer 34

tiredness, drugs, distractions

Question 35

what affects braking distance?

Answer 35

adverse road conditions (icy or wet), poorly maintained vehicles

Question 36

what happens to the kinetic energy of a car if its velocity doubles?

Answer 36

it quadruples (x4)

Question 37

what are the energy transfers involved with braking a vehicle?

Answer 37

the kinetic energy is transferred to thermal energy in the brakes due to the friction between the wheel and the brake the temperature increases and the car slows down

Question 38

if the speed of a car is increased, what happens to the braking force required to stop the car in a given distance?

Answer 38

the braking force increases

Question 39

what can rapid deceleration cause in a car?

Answer 39

the brakes can overheat the driver can lose control very quickly

Question 40

what is an elastic object?

Answer 40

an object which returns to its original shape when the forces deforming it are removed

Question 41

what are the conditions for elastic deformation?

Answer 41

an elastic material, at least two forces acting on the object

Question 42

what would happen if only one force is applied to an elastic object?

Answer 42

the stationary object would move instead of being elastically deformed as the forces are no longer balanced

Question 43

what is an inelastic material?

Answer 43

a material which does not return to its original shape when the forces deforming it are removed

Question 44

what is inelastic deformation?

Answer 44

when an inelastic object has forces exerted on it and does not return to its original shape

Question 45

what is Hooke's law?

Answer 45

the extension of a spring is directly proportional to the force applied as long as the limit of proportionality is not exceeded

Question 46

what is the limit of proportionality of a spring?

Answer 46

the limit for Hooke's law applied to the extension of a stretched spring it is when the spring no longer returns to its original length

Question 47

what is the spring constant of a spring?

Answer 47

the force per unit extension needed to extend the spring. it is a measure of the stiffness of the spring