Recent content by mattgad

I did actually mean to put mb^2 / 6 in my first post. Thanks for replies. Last night I managed to get it myself as well after spotting errors in my work. Thanks.

Homework Statement Calculate the moment of inertia of a uniform triangular lamina of mass m in the shape of an isosceles triangle with base 2b and height h, about its axis of symmetry. The Attempt at a Solution I've tried various things for this and never get the correct answer...

Homework Statement A projectile of mass m is projected vertically upwards with speed U. In addition to its weight it experiences a resistive force mkv^2, where v is the speed at which the projectile is moving and k is a constant. Derive the equation of motion of the projectile: dv/dt =...

So that's all there is to it? For some reason I thought it would be much more complex than this. My knowledge of physics/mechanics is very very limited. I'm actually not sure I even understand the concept of angular speed.

Thanks for your replies guys. I end up with v = root(a*g*root(3)).

Homework Statement Two particles of masses m and 2m are connected by a light inextensible string, which is threaded through a fixed smooth ring. If the lighter particle moves uniformly round a horizontal circle of radius a, while the other particle remains stationary, find the lighter...

I would assume that too, but I'm not too sure. I'm not sure how to proceed with that.

Thanks for your input, although I thought you could only use v = u + at when acceleration is constant. Anyone else?

E(4) is 4, yes. So E(4)+4E(X)+Var(X)+E(X)^2 = 4 + 4*2 + 3 + 2^2 = 19

E(4+4X+X^2) = E(4) + 4E(X) + Var(X) + E(X)^2, as we discussed, I'm not sure where you've got your above equation from.

You've got to plug in the numerical values you know for E(4), E(X), Var(X) and E(X^2) to get a numerical answer.

All your doing is working out the value of E[4+4X+X^2], and your using the fact that E(X^2) = 7 to help you, your not equating anything to 7.

Your not 'solving' I don't know where your getting this 7 from? E(4)+E(4X)+E(X^2), as you've stated, is E(4) + 4E(X) + E(X^2), which is E(4) + 4E(X) + Var(X) + E(X)^2, all of which you have values for. Again, you've said E(X^2) = E(4), here your saying X = 2, but X is a random variable...

No, in your working, the brackets are in the wrong place, and you've ended up saying X = 2 in the first part, rather than E(X) = 2. Use the equations mathman said, rearrange your Var(X) equation to get E(X^2) = Var(X) + E(X)^2, and from there, its just plugging in what you already know.

Homework Statement A bullet of mass 0.03kg is fired from a gun with a horizontal velocity of 400 ms^-1. Find the momentum of the bullet after it is fired. If the gun is then brought to rest in 1.2s by a horizontal force which rises uniformly from zero to B N and then falls uniformly to...