Chapter 3.5 - Newton's Laws of Motion

Question 1

Newtons 1st law

Answer 1

A body will remain at rest or continue to move in a straight line at a constant velocity unless an external force acts on it

Question 2

Newtons 2nd law

Answer 2

The resultant force on an object is directly proportional to the rate of change of momentum of the object and the momentum change takes place in the same direction as the force

Question 3

Newtons 3rd law

Answer 3

If object A exerts a force on object B, then object B will exert an equal and opposite force on object A

Question 4

Equation for momentum

Answer 4

p=mv

Question 5

Rate of change of momentum

Answer 5

Net force

Question 6

In what way is F=ma a special case of F=Dp/Dt

Answer 6

F=ma is F=Dp/Dt but where the mass remains constant

Question 7

Conservation of momentum

Answer 7

Assuming that no external forces act, total momentum is always conserved

Question 8

Two equation for impulse

Answer 8

I=Ft

I=mv-mu

Question 9

How is impulse related to momentum

Answer 9

It equals change in momentum

Question 10

Area under a force time graph

Answer 10

Impulse

Question 11

Rules for elastic collision

Answer 11

Momentum conserved

Kinetic energy conserved

Question 12

Rules for inelastic collision

Answer 12

Momentum conserved

Kinetic energy not conserved

Question 13

When can F=ma not be used

Answer 13

When objects are travelling close to the speed of light (resulting in their mass changing)

Question 14

The essence of all car crash safety features

Answer 14

Increasing the time that it takes for the car and passengers to change their speed. This results in a lower force for the same impulse

Impulse ( P ) = Force x time

Question 15

Crumple Zone and its effects (2)

Answer 15

Areas at the front of the car that crumple upon impact

• Absorb some kinetic energy by deforming
• Increase the time it takes for the car to slow down which reduces the forces on the passengers

Question 16

Air Bags and their effects (2)

Answer 16

Cushions that inflate upon collision

• Make passengers slow down more gradually
• Stop passengers from hitting the dashboard

Question 17

Effects of a seat belt (3)

Answer 17

• Holds the wearer in place
• Absorb some kinetic energy by stretching
• Increase the time it takes to come to a stop

Question 18

How forces in a crash are analysed

Answer 18

Crash tests

Question 19

Risks of seat belts (2)

Answer 19

• Can cause bruising

- If the top part of the belt is placed across the neck in can cause injury in the event of a crash

Question 20

Risks of air bags (2)

Answer 20

• If a passenger is not secured by a seatbelt then the airbag can hit the passenger hard
• Can throw a rear facing child seat towards the car seat