Momentum

Momentum

KNOWLEDGE CHECK

WHAT DID YOU LEARN FROM THE READING YESTERDAY

Multiple Choice

Momentum is equal to

• one half mass times velocity squared

• mass

• mass times velocity

• mass divided by velocity

Multiple Choice

the symbol for momentum is

• m

• $\overrightarrow{p}$
  

• s

• $\overrightarrow{v}$
  

Multiple Choice

momentum is a

• vector

• scalar

• force

Momentum

• defined as " a measure of how difficult it would be to stop a moving object"

• defined as mass times velocity

• symbol:   $\overrightarrow{p}$  

• unit:  kilogram-meter per second

CONSERVATION OF MOMENTUM

• 2nd big conservation law in Physics (after Conservation of Energy)

• The total momentum of a system of objects remains constant.

• Very useful in observing collisions and explosions.

IMPULSE

• Impulse defined as Force times time.

• A large impulse can happen with a small force - exerted for a long time OR over a short time with a very large force.

• Symbol :  $\overrightarrow{J}$  

• Unit:  Newton-second

IMPULSE

• Impulse ALSO equal to CHANGE in momentum

•  $\overrightarrow{J\ }\ =\ \ \overrightarrow{F}\ \cdot t\ =\ \Delta\ \overrightarrow{p}\ \$  

Multiple Choice

A 10,000 kg train is moving at 20 m/s. What is its momentum?

• 500

• 10,0000

• 200,000

• 2,000,000

Multiple Choice

A 10,000 kg train is moving at 20 m/s. It has a momentum of 200,000 kgm/s. Superman jumps in front of the Train and stops the train. What impulse does superman deliver to the train.

• 0

• -200,000

• cannot tell without knowing superman's force

• cannot tell without knowing how long it takes to stop the train.

Multiple Choice

A 10,000 kg train is moving at 20 m/s. It has a momentum of 200,000 kgm/s. Superman jumps in front of the Train and stops the train. If superman exerts a force of 50,000 N - how long does it take the train to stop?

• 4 seconds

• 5 seconds

• 20 seconds

• 25 seconds

Momentum Summary

• momentum is mass times velocity, indication of how hard it is to stop an object

• Impulse is force times time; Impulse is also equal to change in momentum.

• Individual objects change momentum any time there is a net force, but the total amount of momentum does not change.

• Momentum and Impulse will be useful in analyzing collision problems