14 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.
pbefore = pafter
pbefore = 0
Therfore pafter = 0
Therefore the cannon has to move to the left to cancel with the momentum of the cannon ball to the right.
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 1 kg ball moves to the right at 6m/s and hits a wall. It rebounds at 4m/s. to the left
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 = pfinal - pinitial
change in momentum = [1 x (-4)] - [1 x (+6)]
change in momentum = -4 kgm/s - 6 kgm/s
change in momentum = -10 kgm/s
Change in momentum is negative therefore this indicates that the direction of force which caused this change is to the left as well.
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
pbefore = pafter
[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
mbefore x vbefore =mafter x vafter
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
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
If a person on a skateboard pushes on a wall. Name the N3L pair force of….
Persons’ force on wall [left]
Walls’ force on person [right]