# 1 Momentum, N3L and suvat Flashcards

1
Q

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?

A
• 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
2
Q

What is different about N3L pair forces?

A
• they act in different directions
• they act on different objects
3
Q

What is the equation for impulse?

A
4
Q

Is momentum a vector quantity?

A

Yes- it has both magnitude and direction

5
Q

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

A

pbefore = pafter

pbefore = 0

Therfore pafter = 0

[Mcannon x v cannon] + [mcannon ball x Vcannon ball]= 0

[Mcannon x v cannon] = - [mcannon 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

6
Q

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?

A

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.

7
Q

Define momentum

A

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

mass in motion!!!

8
Q

Name the N3L pair force for the force named below

A

The water pushes up and forward on the swimmer

9
Q

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?

A

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.

10
Q

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

A
• 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
11
Q

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

A

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*
12
Q

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

A

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.

13
Q

Define force in terms of momentum

A

Force is the rate of change of momentum

14
Q

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

A

F t = change in momentum

This is called impulse

The area of a force-time graph is the impulse

15
Q

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

In which case is the change in momentum the greatest?

A

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

16
Q

If a person on a skateboard pushes on a wall. Name the N3L pair force of….

Persons’ force on wall

A

Walls’ force on person

17
Q

What is the relationship between momentum, mass and velocity?

A

p=mv

Momentum = mass x velocity

18
Q

When a person runs they exert a back and downwards force on the road surface. Name the N3L pair of this force….

Runner pushes back and down on the road

A

Road pushed up forwards and up on the runner

19
Q

What is the unit for momentum?

A

kgm/s

20
Q

What is the total momentum before the explosion?

What is the total momentum after the collsion

A

zero before and after!!

21
Q

What effect does a crumple zone have on the impact force felt by a driver of a car?

A
• crumple zone 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
22
Q

Is mass a vector quantity?

A

NO-it is a scalar quantity- it only has magnitude (You can’t cancel mass)

23
Q

A catapult can be attached to a cart. If a ball is launched from the heavy cart, the cart moves in the opposite direction.

Using N3L the force on a ball by the cart (catapult) is equal and opposite to the force on the cart by the ball (catapult)

Use this idea of N3L to explain why the velocity of heavy cart is significally smaller than the velocity of the ball

A

F = ma

Since the mass of the ball is significantly smaller than the cart, the velocity of the cart must be significantly smaller than the velocity of ball so that the product of the mass and velocity are equal in magnitude.

24
Q

What effect does bending your legs when landing a parachute jump have on the force felt by the persons legs?

A
• bending legs increases the collision time
• F = (change in momentum)/ time
• Larger collision time for the same change in momentum
• decreases the impact force on the legs
• Less force, less injury
25
Q

Name the N3L pair force

A

air exerts an upward force on the wings

26
Q

What is the unit for mass?

A

kg

27
Q

A person and an elephant are having a tug-o-war. They both pull with 500N.

If the person pulls on the rope with 500N to the left, name the N3L pair force and determine the tension in the rope?

A

The rope pulls on the person with 500N to the right

The tension in the rope is still only 500N! (It is no different if the rope is tied to a wall)

28
Q

Is velocity a vector quantity?

A

Yes- it has both magnitude and direction

29
Q

What is the unit for velocity?

A

m/s

30
Q

Define impulse

A

Impulse is the change in momentum of an object

31
Q

In the suvat equation

v2=u2+2as

What do the symbols stand for?

A
32
Q

Calculate the total momentum before the collsion

A

Only one of the curling stones is moving…therefore

Momentum before = 18 kg x +3 m/s

momentum before = 54 kgm/s [right]

33
Q

What equation can we use which links initial and final speed, acceleration and distance travelled.

A
34
Q

State Newton’s Third Law

A

For every action (force) there is an equal and opposite reaction (force)

35
Q
A

initial velocity = 0 m/s

v2=u2+2as

v2=02+(2x4x60)

v2=480

v=21.9 m/s

36
Q

What is the same about N3L pair forces?

A
• same magnitude
• same type of force
• they act along the same line