Why do internal forces NOT change the momentum of the SYSTEM?

Because internal forces are always balanced

What is FALSE of an external force?

It causes an unbalanced force in the universe

Why will the centre of mass be directly below the hanging point?

Because gravity does not cause net torque in this position

Why do we even CARE about the velocity of the COM?

Because it sums up the motion of the whole system in one vector

The velocity of the COM is...

A kind of average velocity of the system

What can change the velocity of the COM?

An external force acting on the system

Which of these is NOT a good strategy for solving translational motion problems?

Using simultaneous equations to solve for momentum

Why is centre of mass also called centre of gravity?

Because it as if gravity acts at this point

What is the equation for centre of mass in the vertical direction?

yCOM = (m1y1 + m2y2)/total mass

The centre of mass can also be thought of as:

The balance point of the system

How do we find the momentum of a system?

Add the momentum vectors of each object in the system

What is TRUE of an internal force?

It is a force exchanged between objects in the system

How are the momentum and centre of mass concepts linked?

conservation of velocity of COM

If you hang an object up, the centre of mass...

Will be directly below the hanging point

Why is momentum conserved in an explosion?

Because all forces are exchanged within the object exploding

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Translational Motion Recap

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Questions 30

Answers

1
Why do internal forces NOT change the momentum of the SYSTEM?
Because only external forces can change an object's momentum
Because they are not real forces
Because internal forces are always balanced
Because internal forces do not act on anything
2
What is FALSE of an external force?
It is exerted by an object outside the system
It causes an unbalanced force in the system
It causes an unbalanced force in the universe
It changes the momentum of the system
3
Why will the centre of mass be directly below the hanging point?
Because PHYSICS
Because the COM is always at the centre of an object
Because the centre of mass changes depending on where the object is hung
Because gravity does not cause net torque in this position
4
Why do we even CARE about the velocity of the COM?
So we can confuse our friends our whānau for fun
Because it makes us feel like real physicists
Because Mr M told us to
Because it sums up the motion of the whole system in one vector
5
True or false: momentum is conserved in an explosion
False
True
6
The velocity of the COM is...
The velocity of the fastest object in a system
π
The velocity of the biggest mass in the system
A kind of average velocity of the system
7
What can change the velocity of the COM?
Nothing
An explosion of an object in the system
An external force acting on the system
A collision between objects in the system
8
True of false: the position of a system's COM, relative to earth, will change if you choose a different reference point
True
False
9
How do we work out the velocity of the COM?
vCOM = psystem/total velocity
vCOM = psystem/total mass
vCOM = total velocity/total mass
vCOM = total momentum
10
True or false: the COM position is always measured from a chosen reference point
True
False
11
Which of these is NOT a good strategy for solving translational motion problems?
Using simultaneous equations to solve for momentum
Adding vectors geometrically
Breaking down the problem into horizontal and vertical components
Using conservation of momentum laws
12
Why is centre of mass also called centre of gravity?
Because there is zero gravity at this point
Because this point experiences the most gravity
Because this point has the most mass
Because it as if gravity acts at this point
13
What is the equation for centre of mass in the vertical direction?
xCOM = (m1+m2)(x1+x2)/total mass
xCOM = (m1x1 + m2x2)/total mass
yCOM = (m1y1 + m2y2)/total mass
yCOM = (m1+m2)(y1+y2)/total mass
14
Centre of mass is also called...
centre of gravity
centre of force
centre of momentum
centre of oomph
15
True or false: the momentum of individual objects in a system can change due to internal forces
True
False
16
How do we find the momentum of an object?
use the ooomphmeter
p = ma
p = mv
p = pf - pi
17
Impulse tells us...
The amount of force
The amount of ooomph
The amount of momentum
The change in momentum
18
True or false: you always have to calculate the x and y coordinates of 2D COM separately
True
False
19
The centre of mass can also be thought of as:
The point where the system is connected to something else
The point where mass is at a maximum
The balance point of the system
The fastest moving point in the system
20
True or false: Impulse is a scalar
False
True
21
If two objects collide, the impulse exerted on each is...
Equal and in the same direction
0
Different from each other
Equal and opposite
22
How do we find the momentum of a system?
Add the momentum values of each object in the system
Multiply the total mass by the sum of the velocities
Add the momentum vectors of each object in the system
Ask a friend
23
What is TRUE of an internal force?
It is a force exerted by an object outside the system
It is a force exchanged between objects in the system
It is a force which happens inside an object in the system
It is a force that affects all the objects in a system equally
24
How are the momentum and centre of mass concepts linked?
COM = total momentum
there is no link
conservation of velocity of COM
Conservation of COM
25
If you hang an object up, the centre of mass...
Will be at the hanging point
Will be directly below the hanging point
Will not be in line with the hanging point
Could be anywhere
26
When can you just add and subtract momentum values without worrying about vectors?
When an object has 0 momentum
When all motion is in 1D
When all motion is in 2D
When there's only one object in the system
27
If you don't do your homework...
You will have to walk round the class while everyone chants 'shame'
You will get ebola
You will fail Physics
MKZ will have a brain aneurysm
28
Why is momentum conserved in an explosion?
Because all forces are exchanged within the object exploding
Because we need a collision for momentum to change
It's not
Because there was no momentum to begin with
29
What is FALSE if a net force acts at the centre of mass?
The object's COM will stay constant
There will be no rotational motion
There will be net torque
There will be translational motion
30
A longer collision means...
No forces are exchanged
The forces exchanged are unchanged
Lesser forces are exchanged
Greater forces are exchanged

Translational Motion Recap Flashcards | StudBud