Calculating Momentum

Momentum

(excellence) The black ball is initially stationary. Both balls are 0.50 kg. From the diagram, can you calculate the white ball’s initial velocity? (enter answer next slide)

Multiple Choice

The white ball's v_i is :

• 3.2 ms^-1 to the right

• 3.0 ms^-1 to the right

• 2.8 ms^-1 to the right

• 3.5 ms^-1 to the right

Fill in the Blanks

The change in momentum of anything is its final momentum minus its initial momentum.

$\Delta p=p_f-p_i$  
momentum is a ……………………… so direction is important

Multiple Choice

Calculate the momentum change when a 0.50 kg ball moving at 8.5 ms^-1 is stopped by a goalie.

• 4.25 kgms^-1

• 4.25 kgms^-1 opposite to initial momentum

• 4.25 kgms^-1 same direction as initial momentum

Fill in the Blanks

Impulse is a useful concept that relates force to momentum.It is the amount of force, multiplied by time it is exerted. Starting with Newton's 2nd Law of motion : Force is equivalent to the rate of change of

So that impulse =
$F\Delta t\ =\ \Delta p$  

Multiple Choice

A 200g golf ball is whacked at 40ms^-1. The collision lasts 0.0050s.

a) Calculate the momentum change of the ball.

b) Calculate the average force on the ball.

c) Determine the average force on the club.

• a) 8.0 Ns b) 1600 N c) 1600N

• a) 8000 Ns b) 1600 000 N c) 1600 000N

• a) 8.0 Ns b) 160 N c) 160N

• a) 8000 Ns b) 16000 N c) 16000 N

Fill in the Blanks

When a cricketer catches a fast moving ball, they try to make it a “soft catch” This means they move their hands with the ball as it makes contact with their hand. This ................... the time of collision which .................. the size of the force.

Fill in the Blanks

A common road safety message is “ The faster you go the bigger the mess” It is more accurate to say “ The faster you ………... the bigger the mess!!”

Fill in the Blanks

One of the reasons momentum is so useful is that in any interaction, (collision, explosion etc), the momentum always remains ................ if there are no external ...............

(This is true in any particular direction - so collisions in 2-D can be simplified into x and y directions)

Two rugby players collide in a tackle and stick together as shown. Calculate their final momentum and their final velocity.

(enter your answer next slide)

Multiple Select

The rugby players

• Total p = 500 kg m s^-1 bearing 53^o

• Total p = 500 kg m s^-1 bearing 37^o

• Final v = 2.5 ms^-1 bearing 53^o

• Final v = 2.5 ms^-1 bearing 37^o

(excellence) The black ball is initially stationary. Both balls are 0.50 kg.

Calculate the white ball’s final velocity. (enter next slide)

Multiple Choice

White ball's v_f is:

• 3.2 ms^-1 bearing 65⁰

• 3.0 ms^-1 bearing 65⁰

• 3.0 ms^-1 bearing 55⁰

• 3.2 ms^-1 bearing 55⁰