1 Momentum, N3L and suvat

Question 1

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?

Answer 1

• 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

Question 2

What is different about N3L pair forces?

Answer 2

• they act in different directions
• they act on different objects

Question 3

Is momentum a vector quantity?

Answer 3

Yes- it has both magnitude and direction

Question 4

Define momentum

Answer 4

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

mass in motion!!!

Question 5

Name the N3L pair force for the force named below

Answer 5

The water pushes up and forward on the swimmer

Question 6

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

Answer 6

• 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

Question 7

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

Answer 7

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*

Question 8

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

Answer 8

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.

Question 9

Define force in terms of momentum

Answer 9

Force = change of momentum / time

Question 10

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

Answer 10

F t = change in momentum

This is called impulse

The area of a force-time graph is the impulse

Question 11

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?

Answer 11

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

Question 12

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

Persons’ force on wall

Answer 12

Walls’ force on person

Question 13

What is the relationship between momentum, mass and velocity?

Answer 13

p=mv

Momentum = mass x velocity

Question 14

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

Answer 14

Road pushed up forwards and up on the runner

Question 15

What is the unit for momentum?

Answer 15

kgm/s

Question 16

What is the total momentum before the explosion?

What is the total momentum after the collsion

Answer 16

zero before and after!!

Question 17

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

Answer 17

• 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

Question 18

Is mass a vector quantity?

Answer 18

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

Question 19

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

Answer 19

• 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

Question 20

Name the N3L pair force

Answer 20

air exerts an upward force on the wings

Question 21

What is the unit for mass?

Answer 21

kg

Question 22

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?

Answer 22

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)

Question 23

Is velocity a vector quantity?

Answer 23

Yes- it has both magnitude and direction

Question 24

What is the unit for velocity?

Answer 24

m/s

Question 25

Define impulse

Answer 25

Impulse is the change in momentum of an object

Question 26

In the suvat equation

v²=u²+2as

What do the symbols stand for?

Answer 26

Question 27

Calculate the total momentum before the collsion

Answer 27

Only one of the curling stones is moving…therefore

Momentum before = 18 kg x +3 m/s

momentum before = 54 kgm/s [right]

Question 28

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

Answer 28

Question 29

State Newton’s Third Law

Answer 29

If object A exerts a force on object B,

then

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

Question 30

Answer 30

initial velocity = 0 m/s

v²=u²+2as

v²=0²+(2x4x60)

v²=480

v=21.9 m/s

Question 31

What is the same about N3L pair forces?

Answer 31

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