Centripetal Force (1 Viewer)

[shantu1992]

1. a mass of 1.6 kg moves in a circle of radius 22.0 cm at 3 revs/ second. calculate

(a) the tangential force
(B) the centripetal acceleration
(c) the centripetal force

2. a bob of mass 6.0 kg is attatched to a light inextensible, string of length .500 m. it is then caused to describe uniform circular motion about the other end of the string, which is fixed. the bob completes 40 revs every minute. calculate the following

(a) the period f the motion
(b) the centripetal acceleration of the bob
(c) the centripetal force acting on the bob

 

[cutemouse]

3 revs/ second.

Isn't that 6 radians per seconds, the angular velocity, which is no longer in the HSC Physics Course?

Where did you get this question from?

 

[Almatari]

@jm01 : you missed out the "π"
3 rev/sec = 3x2π radians/sec, but you don't need this in physics, only in 4Unit maths and you MUST NEVER use maths methods for physics for vice versa


linear velocity: v=distance/time
for circular velocity: v=circumference/time
thus circular velocity: v= 2πr/T , where T=period (time taken for one revolution)

Also centripetal force Fc=mv^2/r

Also since f=ma, you should notice centripetal acceleration = v^2/r

Note that centripetal acceleration and Fc acts towards the centre of motion

 

[Almatari]

I'm not sure but I'll try answering it...

Question1:
r=22.0cm = 0.022m
3 rev/sec --> T=1/3 sec
centripetal velocity v = 2πr/T = 2π (0.022) x3 = 0.132π m/s
**Centripetal acceleration = v^2/r = (0.132π)^2 / 0.022 = 6π^2 m/s^2 towards the centre of motion
**centripetal force = ma =1.6 x 6π^2 = 9.6π^2 N towards the centre of motion

I think you can work the rest out yourself
I hope this helps

 

[cutemouse]

So you're saying we can't use any algebra or trigonometric functions?

@jm01 : you missed out the "π"
3 rev/sec = 3x2π radians/sec, but you don't need this in physics, only in 4Unit maths and you MUST NEVER use maths methods for physics for vice versa

 

[Almatari]

So you're saying we can't use any algebra or trigonometric functions?

Of course you need simple algebra and trig for physics.

I'm just saying what is required for physics and ext2 maths is different.

For example in projectile motion, in physics you're required to solve problems using the equations of motion v=u+at......
While in maths, you're required derive another set of equations from differentiating vertical acceleration=-g and horizontal acceleration=0

Note v=u+at etc are derived from these maths equations BUT it is not required in the syllabus, thus there is a distinctive "physics" method and a "maths" method to solve a problem

 

[cutemouse]

Actually, you can use 'Maths methods', just sub the values in the 'maths equations'.

This is from a Physics/Maths teacher who was a Senior Marker.