Prelim Physics Thread (2 Viewers)

[Green Yoda]

Welcome to the physics thread
This thread can be used for help or to test other people!

I'll start off:
Draw a diagram of a car moving at constant velocity and label all the forces acting upon it. (3 marks)
Write a statement that describes the net force on the car. (1 mark)

 

[leehuan]

I promise I won't do too many questions

Assuming we're not on a ramp.

Am I missing any forces?
- Gravity
- Normal reaction from ground
- Friction
- Thrust

 

[Green Yoda]

I promise I won't do too many questions

Assuming we're not on a ramp.

Am I missing any forces?
- Gravity
- Normal reaction from ground
- Friction
- Thrust

Sorry Forgot to mention, going up a ramp

 

[eyeseeyou]

I promise I won't do too many questions

Assuming we're not on a ramp.

Am I missing any forces?
- Gravity
- Normal reaction from ground
- Friction
- Thrust

Why do these forces act upon a car?

 

[leehuan]

Why do these forces act upon a car?

We're assuming that the car is going up the ramp at a constant velocity.

Suppose thrust is missing.

Then naturally we have gravity forcing the car to stay on the ramp and not start floating into the air
A normal reaction force from the ramp so that the car doesn't fall through the ramp
And unless the ramp is the frictionless surface, there always is friction due to contact between two objects.

However, these forces alone will mean that the car will slowly decelerate down the ramp.

We need a thrust force to ensure that the car constantly moves upwards instead.

 

[Green Yoda]

We're assuming that the car is going up the ramp at a constant velocity.

Suppose thrust is missing.

Then naturally we have gravity forcing the car to stay on the ramp and not start floating into the air
A normal reaction force from the ramp so that the car doesn't fall through the ramp
And unless the ramp is the frictionless surface, there always is friction due to contact between two objects.

However, these forces alone will mean that the car will slowly decelerate down the ramp.

We need a thrust force to ensure that the car constantly moves upwards instead.

yup pretty much, but instead of gravity weight would be better as for calculations you can use wsinθ

 

[InteGrand]

yup pretty much, but instead of gravity weight would be better as for calculations you can use wsinθ

With gravity, it instead becomes mg.sin(θ), where m is the mass of the car.

(But yes, technically gravity isn't the force (I think), but rather the cause of a force; we should say "force due to gravity", aka weight.)

 

[Green Yoda]

With gravity, it instead becomes mg.sin(θ), where m is the mass of the car.

(But yes, technically gravity isn't the force; we should say "force due to gravity", aka weight.)

Basically the weight haha

 

[eyeseeyou]

With gravity, it instead becomes mg.sin(θ), where m is the mass of the car.

(But yes, technically gravity isn't the force (I think), but rather the cause of a force; we should say "force due to gravity", aka weight.)

why

 

[leehuan]

True. Weight does sound more befitting

why

We're inclined at an angle. We don't feel the entire weight force acting down.

 

[eyeseeyou]

We're assuming that the car is going up the ramp at a constant velocity.

Suppose thrust is missing.

Then naturally we have gravity forcing the car to stay on the ramp and not start floating into the air
A normal reaction force from the ramp so that the car doesn't fall through the ramp
And unless the ramp is the frictionless surface, there always is friction due to contact between two objects.

However, these forces alone will mean that the car will slowly decelerate down the ramp.

We need a thrust force to ensure that the car constantly moves upwards instead.

why

 

[Green Yoda]

why

Driving force..to keep the car moving up the ramp..NO thrust = no velocity so it will roll down

 

[eyeseeyou]

Hey guys

Is it alright if I constantly ask "why" and annoy the hell out of you, just to test your knowledge and improve mine?

 

[Green Yoda]

Hey guys

Is it alright if I constantly ask "why" and annoy the hell out of you, just to test your knowledge and improve mine?

ofc..ur why is the most important

 

[Green Yoda]

Write a statement that describes the net force on the car. (1 mark)

.

 

[leehuan]

I deliberately left that question alone lol but the idea is that all the forces cancel out because the car moving at a constant velocity implies zero acceleration.

And F=ma

 

[Green Yoda]

I deliberately left that question alone lol but the idea is that all the forces cancel out because the car moving at a constant velocity implies zero acceleration.

And F=ma

note: ΣF=ma is the same thing but this one implies net force. But yeah the answer should be obvious now..

 

[eyeseeyou]

Driving force..to keep the car moving up the ramp..NO thrust = no velocity so it will roll down

But why would no thrust mean no velocity, therefore making it slow down?

 

[eyeseeyou]

I deliberately left that question alone lol but the idea is that all the forces cancel out because the car moving at a constant velocity implies zero acceleration.

And F=ma

Why would moving at a constant velocity imply zero acceleration?

 

[eyeseeyou]

Oh yeah, where is F=MA derived from?