Newton's Laws

Question 1

newton’s first law of motion

Answer 1

a body will remain at rest or continue to move with constant velocity if the forces acting on it are balanced

Question 2

what is inertia?

Answer 2

The tendency of an object to continue in its current state (at rest or in uniform motion/ constant velocity) unless acted on by a resultant force.

Question 3

if an object is stationary or already moving and a resultant force acts on the object it will…

Answer 3

accelerate in the direction of the resultant force

Question 4

what equation is related to newton’s second law?

Answer 4

• f=ma
• resultant force(N)= mass(kg) x acceleration (m/s2)

Question 5

what is newton’s second law?

Answer 5

the acceleration of a body is proportional to the resultant force causing it’s acceleration and is in the same direction. it is also inversely proportional to the mass of the object

Question 6

what is inertial mass?

Answer 6

a measure of how difficult it is to change the velocity of an object (just the mass in the f=ma equation)

Question 7

when asked to estimate accelerations, forces etc. of a large vehicle, what symbol must you use (this symbol is also used in the values given in the question)?

Answer 7

~ before the number

Question 8

what is newton’s third law?

Answer 8

when body A exerts a force on body B, body B exerts an equal and opposite force on body A OR whenever two objects interact, they exert equal and opposite forces on each other.

Question 9

what 4 factors can affect a driver’s reaction time/ thinking distance?

Answer 9

• tiredness
• drugs
• alcohol
• distractions

Question 10

describe a method used to measure human reaction times

Answer 10

One simple method involves dropping a ruler between someone’s open thumb and forefinger. The higher the reaction time needed to grasp the falling ruler, the further the ruler falls before being stopped.

Question 11

what 2 factors affect braking distance?

Answer 11

• poor road and weather conditions, such as wet or icy roads
• poor vehicle conditions, such as worn brakes or worn tyres

Question 12

what is total stopping distance made up of?

Answer 12

reaction time/ thinking distance + breaking distance

Question 13

when might stopping distances be relevant?

Answer 13

In an emergency, a driver must bring their vehicle to a stop in the shortest distance possible

Question 14

what is a typical reaction time in between?

Answer 14

between typically 0.2 s and 0.9 s

Question 15

what are the implications for road safety of braking distance/ speed?

Answer 15

• The faster a vehicle travels, the greater the braking force needed to stop it in a certain distance.
• A greater braking force produces a greater deceleration.
• Large decelerations may cause the brakes to overheat, and the driver may also lose control of the vehicle.

Question 16

what happens when a braking force is applied to the wheel?

Answer 16

• When a force is applied to the brakes of a vehicle, there is work done by the
  friction between the brakes and the wheel.
• This reduces the kinetic energy of the vehicle, slowing it down and causing the temperature of the brakes to increase.

Question 17

the greater the breaking force…

Answer 17

the larger the deceleration

Question 18

state estimate masses of a car and lorry

Answer 18

• ~1200 kg to ~1600 kg
• ~36,000 kg

Question 19

how do you estimate forces involved in the deceleration of road vehicles?

Answer 19

1. know average speed of a car (30m/s)
2. we are assuming uniform deceleration
3. find deceleration by rearranging v² – u² = 2as to (v² – u²) / 2s = a
4. estimate mass of car which is ~1200kg
5. use f= ma

Question 20

average speed of a car

Answer 20

30 m/s

Question 21

what is momentum measured in?

Answer 21

kg m/s

Question 22

what is the principle of the conservation of momentum?

Answer 22

in a closed system, the total momentum before a collision/ event is equal to the tptal momentum after a collision/ event.

Question 23

is momentum a vector or scalar quantity and why is this important?

Answer 23

Vector, so it is important to consider both magnitude and direction. For example, if travelling east is given a positive value, travelling west is given a negative value.

Question 24

describe an example of momentum in a collision

Answer 24

• During a collision there is a change in momentum.
• The force of the collision is equal to the rate of change of momentum.
• Car safety features such as seatbelts, airbags and crumple zones all work to change the shape of the car, which increases the time taken for the collision.
• Crumple zones refer to the areas of a car that are designed to deform or crumple on impact.
• These different safety features decrease the rate of change of momentum, which decreases the force of the collision on any people within the car.