# 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

Is momentum a vector quantity?

A

Yes- it has both magnitude and direction

4
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!!!

5
Q

Name the N3L pair force for the force named below

A

The water pushes up and forward on the swimmer

6
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
7
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*
8
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.

9
Q

Define force in terms of momentum

A

Force = change of momentum / time

10
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

11
Q

The same 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

12
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

13
Q

What is the relationship between momentum, mass and velocity?

A

p=mv

Momentum = mass x velocity

14
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

15
Q

What is the unit for momentum?

A

kgm/s

16
Q

What is the total momentum before the explosion?

What is the total momentum after the collsion

A

zero before and after!!

17
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
18
Q

Is mass a vector quantity?

A

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

19
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
20
Q

Name the N3L pair force

A

air exerts an upward force on the wings

21
Q

What is the unit for mass?

A

kg

22
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)

23
Q

Is velocity a vector quantity?

A

Yes- it has both magnitude and direction

24
Q

What is the unit for velocity?

A

m/s

25
Q

Define impulse

A

Impulse is the change in momentum of an object

26
Q

In the suvat equation

v2=u2+2as

What do the symbols stand for?

A
27
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]

28
Q

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

A
29
Q

State Newton’s Third Law

A

If object A exerts a force on object B,

then

object B will exert an equal and opposite force on object A

30
Q
A

initial velocity = 0 m/s

v2=u2+2as

v2=02+(2x4x60)

v2=480

v=21.9 m/s

31
Q

What is the same about N3L pair forces?

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