How Do You Solve Particle Motion Problems in Physics Exams?

[Woolyabyss]

Homework Statement

So I just sat an exam today and I'm not sure how I did in this question. I think I did bad in it.

http://www.examinations.ie/archive/exampapers/2014/LC020GLP000EV.pdf

Its question 8

Homework Equations

F = mv^2/r

v=ωr

t=2(pi)r/v

The Attempt at a Solution

Q9

(a)

T=2(pi)r/v ...... 0.4pi = 2pi(2)/v

solving for v ... 10 m/s

v = rω

10 = 2ω ...... ω = 5 rad/s

a =v^2/r

a = 10^2/2 = 50 m/s^2

(i) 5 rad/s
(ii) 10 m/s
(iii) 50 m/s^2(B)

(i) r = 1sin30 = 0.5m

(ii) splitting its weight into components perpendicular and parallel to string

parallel force = 2gcos30 = √3 g N

Tension = parallel force
Tension = √3 g N

(iii) F = mv^2/r

√3 g = 2v^2/.5
solving for v = 2.06 m/s

v = ωr

2.06 = .5ω

ω = 4.12 rad/s

 

[BiGyElLoWhAt]

hmmm... well what exactly are you looking for? someone to check your work? If you're looking for that, the LEAST you can do is keep it all algebraic (symbolic) until the end. Too many numbers here.

That being said, I didn't work through the first one, but ii) in solving for the tension, your setup is wrong, which means you probably got the wrong answer. What do you know about the vertical acceleration if it's constrained to moving along that circle? What is the value of that component?

Now what else can you say that value is equal to?

 

[BiGyElLoWhAt]

also, you labeled it Q9, not Q8.