Questions 1 - Momentum

1. Work out, giving your answer in kg m/s, the momentum of the following objects:
a) a bowling ball of mass 6kg travelling at 8m/s
m = 6 | P = M x V | = 6 x 8
v = 8  |                  | = 48 kg m/s

b) a ship of mass 50000kg travelling at 3 m/s
m = 50000 | P = M x V | = 50000 x 3
v = 3          |                  | = 150000 kg m/s

2. a) How does an elastic collision differ from partially elastic and inelastic collisions?
An elastic collision is when no kinetic energy is lost as other forms of energy in a collision. There are very few of these. Partially elastic collisions occur when objects rebound, but still lose some of their kinetic energy in doing so. Inelastic collisions are when objects lose a LOT of their kinetic energy as another form of energy in a collision, essentially "sticking" together when they collide.

b) Give an example of:
    i) An elastic collision
Air molecules bumping into each other - they're always moving and bumping, they don't just pile up at the bottom of a container

   ii) An inelastic collision
When two railway trucks collide and both move, together, in the same direction.

4. A rocket of mass 1200kg is travelling at 2000m/s. It fires its engine for 1 minute If the forward thrust by the engine is 10kN (10000 N), what is the increase in momentum of the rocket? From this, work out the increase in velocity of the rocket and its new velocity after firing the engines
P = M x V
= 1200kg x 2000m/s
= 2400000 kg m/s

F = ΔP ÷ T
1 minute in secs = 60 sec
ΔP = F x T
= 10000 x 60
= 600000 kg m/s

Momentum before = 2400000
Momentum after = 2400000 + 600000 = 3000000

Velocity before: 2000m/s
Velocity after: 2500 m/s
P = M x V 
V = P ÷ M
= 3000000 ÷ 1200
= 2500m/s 

Change in velocity: 500m/s :)

1.1 Use the following units: kilogram (kg), metre (m), metre/second (m/s), metre/second2 (m/s2), newton (N), second (s), newton per kilogram (N/kg), kilogram metre/second (kg m/s)

Measurement                      Symbol               What it measures
Kilogram                                  Kg                           Mass
Meter                                        m                       Distance
Meter per second                    m/s                   Velocity/speed
Meter per second squared      m/s^2                 Acceleration
Newton                                         N                           Force
Kilogram meter per second     kg m/s                Momentum
Newton per kilogram               N/kg                     Moment

1.21 Use the idea of momentum to explain safety features

We already know that force felt = change in momentum ÷ time

To decrease the force felt, you would have to increase the amount of time it takes for the force to be felt. In a car, there are various safety features equipped to do this, as they increase the time that the car's momentum takes to reach zero.

Eg crumple zones in cars slow down the time taken for the momentum to be transferred to the passenger

Some safety features include:
• seat belts
• air bags
• crumple zones
All the above reduce injuries deforming and therefore increasing the amount of time it takes for a person to come to a stop, reducing the acceleration and force on the person, so reducing injury :)

Image: drawing of two safety features of the car. (by: me!!) 

(Yeah okay it's not amazing but it gets the message across)

1.20 Know and use the relationship between momentum, mass and velocity

Momentum = Mass x Velocity

P = M x V

P is measured in kg m/s
M is measured in kg
V is measured in m/s