- #1
MickeyGoh
- 7
- 0
Homework Statement
A solid cube of wood with side 2a and mass M is resting on a horizontal surface. The cube is constraint to rotate about a fixed axis AB. A bullet of mass m and speed v is shot at the face opposite ABCD at a height of 4a/3. The bullet becomes embedded in the cube. Find the minimum value of speed v required to tip the cube so that it falls on the face ABCD. Assuming m << M.
2. Homework Equations
I = MR2 (the integral one)
KE = 0.5 mv2
Force*height = Moment of Inertia*angular acceleration
(i am not sure)
The Attempt at a Solution
Actually, I have just learned moment of inertia and rotational motion. And teacher just give me this. I have difficulties in finding moment of inertia of a cube. I just can't get the result something like ms2/6 if the axis passes through center.
I am confused... I know that for a sphere we can make it into a very thin shell that dV = 4 πr2dr
But how can I do it when it comes to cube? The r seems different when it touches the side and the corner?
https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-xpa1/v/t34.0-12/10681646_10203072127269453_1684323490_n.jpg?oh=38647e54fa690c109ae2d505e3bff890&oe=5434F8D3&__gda__=1412758462_e1726fd93896039363a30fbcd178af5e