Daniel's Physics Questions

[danieltennis]

Can you also help me with q5 aswell?

Thanks

[UprightMan]

F = kx; F = 0.75N or 0.735N (if you use g = 9.; x = 0.05M; k = ?

F / k = x
0.735 / 0.05 = k
k = 14.7 N/m
or k = 15 N/m (2 sig figs)

SPE = 1/2 k x²
      = 1/2 * 14.7 * 0.05²
      = 0.018375 J
      or 0.018 J (2 sig figs)

[danieltennis]

SPE = 1/2 k x²
      = 1/2 * 14.7 * 0.05
      = 0.3675 J
      or 0.37J (2 sig figs)

Thanks, but you forgot to square the distance lol

[UprightMan]

Oh woops rofl.  Editted; thanks for picking up that error; I gotta stop doing stupid things like that >_>  it'll cost me in exams if I'm not careful.

[dejan91]

Question 4, (sorry if my handwriting isa bit hard to read):



Dunno if this is the right way to go about it, but who cares, I got the right answer in the end.
Oh, and I use Heinemann physics too, and I checked.

[danieltennis]

Hey,

'At what rate is thermal energy being dissipated in the brakes?'

Can anyone explain what this question means?

Thanks

[TrueTears]

Rate just means power, where E is energy in Joules and t is time in seconds

[danieltennis]

Thanks Truetears

[danieltennis]

hi guys, just need help with this q.

A 10 m long drawbridge is supported by two cables which extend from two holes either side of a door in a castle wall. The bridge has a mass of 700 kg and the tension is the same in both cables. The bridge is just about to touch the ground and the cables make an angle of 30° to the horizontal.

a/ Write an expression for the torque produced by each of the tensile forces that act around the axis of rotation of the bridge.
b/ Write an expression for the horizontal and vertical components of the tension force.
c/ Calculate the size of the tension in each

Your help will be appreciated.

cheers

[TrueTears]

I assume the cables reach the very end of the drawbridge.

a) so the Centre of Mass of the drawbridge is 5 m away from the axis of rotation.

taking clockwise torque as positive and anti clockwise as negative yields

( is the force that ONE cables exert upwards, ie vertically anticlockwise sense.) (3500 because one cable supports half the mass of the bridge)

However the question says TENSILE force, so I guess I have to componentise the tension.

so the vertical component of the tension is . Subbing Tsin(30) back in for yields That is the total torque produced by one tensile force AND the mass of the bridge. Question asks for just torque produced by ONE tensile force

[Over9000]

nice truetears 

[TrueTears]

b)

[uni09]

How do I get a 50 in physics?

Pretty much dominate all SACs and both the exams.

[TrueTears]

c) solving for T :

[danieltennis]

Awesome work TT!

How do I get a 50 in physics?

Pretty much dominate all SACs and both the exams.

WTH! When did I say that?