7 : Laws of motion and momentum

Question 1

momentum

Answer 1

• p = mv
• Kg ms^ -1

Question 2

conservation of momentum

Answer 2

• assuming no external forces
• total momentum before collision equals total momentum after collision
• air rifle ex forward momentu gained = backward momentum of rifle

Question 3

elastic collisions

Answer 3

• momentum and kinetic energy is conserved
• no energy is dissipated as heat or sound

Question 4

impulse

Answer 4

• the rate of change in momentum
• Ns
• average force x time

Question 5

Newton’s 1st law

Answer 5

• velocity of an object will not change unless a net force acts on it
• remain at constant speed or in a straight line- if forces aren’t balanced overall net force will cause an acceleration changing speed or direction

Question 6

Newton’s 2nd law

Answer 6

• the rate of change in momentum od an object is directly proportional to the net force which acts on the object
• F =Δp/Δt
• if mass is constant F = ma

Question 7

Newton’s 3rd law

Answer 7

• if an object A exerts a force on object B, then object B exerts a equal but opposite force on object A
• consequence of conservation of momentum

Question 8

Car crashes

Answer 8

• F= Δp/Δt
• when a car crashes there is a ig change in speed ( to zero)
• therefore there is a big change in momentum
• if it stops quickly the force acting n the car is very large
• Δt can be increased than the force is much smaller so the impact of the force i reduced

Question 9

Crumple zones

Answer 9

• absorb some kinetic energy when they deform this would otherwise be transferred to passengers
• the increase in time taken for car to slow down reduces the force on passengers

Question 10

Air bags

Answer 10

• inflate quickly on impact of collision
• makes passengers slow down more quickly
• stopping passengers from hitting dashboard

Question 11

Seat belts

Answer 11

• holding passenger in place
• absorbing some kinetic energy by stretching
• increasing time taken to stop increasing Δt

Question 12

risks of safety features

Answer 12

• seat belts - creates bruising, children - lies across their neck causing them injury
• airbags - if not wearing seatbelt passengers moves forward quickly as car slows and hit the airbag as t is inflating quickly causing injury