A Couple Physics Questions...

[Comessy]

So I just completed my final test for physics, and there were 2 questions I was unsure of. Maybe you guys could help me out?

I know a lot of you guys have done grade 11 physics before.

Don't bother doing significant digits.
 

1. Spring Potential : Hooke's Law 

 A Force of 12N is required to stretch a spring 4m. How much energy is in the system when it is stretched 6m?

 

 

2. Centripetal motion

A 400kg roller coaster is going around a vertical loop-de-loop. The force normal at the top of the loop is 5000N. The centripetal force remains the same throughout the loop.

-What is the centripetal force at the top of the loop?

-What is the force normal at the bottom of the loop?

[Stardar1]

So I just completed my final test for physics, and there were 2 questions I was unsure of. Maybe you guys could help me out?

I know a lot of you guys have done grade 11 physics before.

Don't bother doing significant digits.

 

1. Spring Potential : Hooke's Law 

 A Force of 12N is required to stretch a spring 4m. How much energy is in the system when it is stretched 6m?

 

 

2. Centripetal motion

A 400kg roller coaster is going around a vertical loop-de-loop. The force normal at the top of the loop is 5000N. The centripetal force remains the same throughout the loop.

-What is the centripetal force at the top of the loop?

-What is the force normal at the bottom of the loop?

Took AP Physics last year (im a junior now).

 

Remember nothing. 

 

so... 

¯\_(ツ)_/¯

[Taswell]

never toook physics but im guessing the answer to the first one is 18n

[Blade of Grass]

Given the force and distance applied to the spring you should be able to figure out the spring constant for it. Then plugin the second distance into the equation to figure out the answer.

[werto165]

E = 1/2 K x^2 or the area under the curve of a F against X graph.  

F  = Kx 

you know that F = 12N and x = 4m so 12 /4 = 3 = spring stiffness you use that to calculate above

 

 

tangential accelearation = 2rdot theta dot  + r theta double dot 

radial acceleation = r double dot - r theta dot^2 

so radial acceleration is the the centripetal force, F = mv^2 /r 

where theta dot = omega or angular velocity. 

doesn't really apply

 

400*9.805 = force and you use the normal force to work out the centripetal force. 

so at the bottom it would be Normal force at the top + 400*9.805. 

[Comessy]

Given the force and distance applied to the spring you should be able to figure out the spring constant for it. Then plugin the second distance into the equation to figure out the answer.

That would give me the force needed to stretch the spring, not the energy in the system

[werto165]

That would give me the force needed to stretch the spring, not the energy in the system

Energy is a Force times an integral of the area for which the force has moved through. 

it's the area under the graph basically. which is a trapesium. 

[Comessy]

E = 1/2 K x^2 or the area under the curve of a F against X graph.  

F  = Kx 

you know that F = 12N and x = 4m so 12 /4 = 3 = spring stiffness you use that to calculate above

 

 

tangential accelearation = 2rdot theta dot  + r theta double dot 

radial acceleation = r double dot - r theta dot^2 

so radial acceleration is the the centripetal force, F = mv^2 /r 

where theta dot = omega or angular velocity. 

doesn't really apply

 

400*9.805 = force and you use the normal force to work out the centripetal force. 

so at the bottom it would be Normal force at the top + 400*9.805. 

 

Ah yes. So would the total energy in the system be 1/2 (3)6^2 = 54N, is this correct?

 

TOP

Fg = 400x9.81 = 3924N

Fn = 5000

Fn + Fg = Fc

5000 + 3924 = 8924N Centripetal force

 

BOTTOM

Fg + Fc = Fn

3924 + 8924 = 12848N

[Blade of Grass]

That would give me the force needed to stretch the spring, not the energy in the system

Correct, refer to @werto165 post for a full solution suggestion.

[Mug]

 

Having done A Level Physics I've never come acress the term force normal so didn't quite know what that meant, so ignore the answer to the second one. @Comessy is correct.

[Comessy]

 

Having done A Level Physics I've never come acress the term force normal so didn't quite know what that meant, so ignore the answer to the second one. @Comessy is correct.

 

In the first question you put "6 x 3 = 9"

 

I believe 6 x 3 = 18

[Mug]

In the first question you put "6 x 3 = 9"

 

I believe 6 x 3 = 18

sorry, it was because 1/2*6*3=9

 

forgot the half. Gah!