# 1 Momentum, N3L and suvat Flashcards

What effect does a cushion on the inside of a helmet have on the impact force felt by a cyclist if they collide with a windscreen?

- cushion increases the collision time
- F = (change in momentum)/ time
- Larger collision time for the same change in momentum
- decreases the impact force
- Less force, less injury

What is different about N3L pair forces?

- they act in different directions
- they act on different objects

What is the equation for impulse?

Is momentum a vector quantity?

Yes- it has both magnitude and direction

Use the conservation of momentum to explain why a cannon would have a recoil velocity when a cannon ball is fired.

p_{before} = p_{after}

p_{before} = 0

Therfore p_{after} = 0

[M_{cannon} x v _{cannon}] + [m_{cannon ball} x V_{cannon ball}]= 0

[M_{cannon} x v _{cannon}] = **-** [m_{cannon ball} x V _{cannon ball}]

*negative sign shows that the cannon must move in opposite direction to cannonball so that their momentum’s cancel out*

If the action and reaction force in the image below are equal an opposite.

Can these forces cancel? Why does the small boat move backwards if these forces are equal and opposite?

The reaction force __acts on the boat__

The action force __acts on the person__

They cannot cancel!

Therefore the reaction force on the boat makes the boat move to the right.

Define momentum

The property an object has due to its mass and velocity. It is the product of its mass and velocity

mass in motion!!!

Name the N3L pair force for the force named below

The __water__ pushes up and forward on the __swimmer__

A 0.8 kg ball moves to the **right** at 6m/s and hits a wall. It rebounds at 4m/s.

How can you calculate its change in momentum and what is the direction of the force which causes this change in momentum?

final velocity is to the left therefore -4m/s

Change in momentum is negative therefore this indicates that the direction of force which caused this change is to the left.

What effect does making a hammer of hard steel have on the impact force on a nail?

- hard steel hammer decreases the collision time
- F = (change in momentum)/ time
- smaller collision time for the same change in momentum
- increases the impact force
- more force, easier to drive in nail

Use the conservation of momentum to create a equation for the collision below

p_{before }= p_{after}

[0.01 kg x 300m/s] + [0] = [(0.01 kg + 1.99kg) x v]

- Note the velocity of the block before is 0m/s*
- After the bullet is in the block and the total mass of the system is 2.00 kg*

Explain why the velocity of the cart decreases after the mass is dropped onto it.

Momentum is conserved

p before = p after

m_{before} x v_{before} =m_{after} x v_{after}

m_{ }V = M v

If the mass of the system increases after the collsion the velocity must decrease to keep momentum the same.

Define force in terms of momentum

Force is the rate of change of momentum

What does the area of a force-time graph represent?

F t = change in momentum

This is called impulse

The area of a force-time graph is the impulse

An object undergoes a change in motion indicated as Case A and Case B.

In which case is the change in momentum the greatest?

Case A- Since mass is the same we can look at the change in velocity.

The change in velocity is found by using

(v-u)

(-3 m/s) - (5m/s)

= -8m/s