ok, I have my assignment due by noon today and it is now 2:00am (I've been up most of tonight trying to get 4 questions done and they are all driving me insane) Of the 4, 3 are dealing with static Equilibrium So if you can Help with ANY of them I'll really appriciate it. 1) A rod of length 68.0 cm and mass 2.00 kg is suspended by two strings which are 38.0 cm long, one at each end of the rod. The string on side B is cut. Find the magnitude of the initial acceleration of end B. A diagram can be found here: http://capaserv.physics.mun.ca/msuphysicslib/Graphics/Gtype20/prob13a_1016full.gif my workings: net force = 0 A + B - mg = 0 and net torque = 0 picking pivot to be at point A LB - mgR = 0 so solving the torque equation to find B = (9.8)(2)(0.34) / (0.68) B = 9.8N so A = 9.8N as well (solving the net force eqn) I'm not even sure if I have that much done right, or even if i had to do that, I guess the length of the strings comes into play somewhere but I haven't used them yet, I need a lot of help with this one I think. 2) A 28.0 kg beam is attached to a wall with a hinge and its far end is supported by a cable. The angle between the beam and the cable is 90°. If the beam is inclined at an angle of theta=13.1° with respect to horizontal, what is the horizontal component of the force exerted by the hinge on the beam? a graphic is here: http://capaserv.physics.mun.ca/msuphysicslib/Graphics/Gtype24/prob19a_beamhinge1.gif so my workings Ty + Fy - mgsin(90-13.1) = 0 Fx - Tx = 0 LTy - L/2 mgsin(90-13.1) = 0 Ty = (9.8)(28)(sin(76.9) / 2 Ty = 133.63 N Tsin76.9 = 133.63N T = 137.20 Tcos76.9 = Tx Tx = 31.1 N Fx - 31.1 N =0 Fx = 31.1 N And this is wrong I know, I really dunno where I've gone wrong but I only have 3 more tries left on this question so I'm getting a little stressed out by it. 3) A sledgehammer with a mass of 2.40 kg is connected to a frictionless pivot at the tip of its handle. The distance from the pivot to the center of mass is r_cm=0.570 m, and the moment of inertia about the center of mass is I_cm = 0.0360 kgm2. If the hammer is released from rest at an angle of theta=59.0 degrees such that H=0.489 m, what is the speed of the center of mass when it passes through horizontal? A graphic: http://capaserv.physics.mun.ca/msuphysicslib/Graphics/Gtype20/prob34_sledgehammer.gif I'm really not sure what to do with this one.... I'm getting really tired and stressed and my concentration is slowly dying... 4) A solid door of mass 33.10 kg is 2.40 m high, 1.00 m wide, and 2.94 cm thick. If the edge of the door has a tangential speed of 45.7 cm/s, what is the rotational kinetic energy of the door? I've already found the Moment of inertia for the door about an axis through it's hinges to be 11 kg*m^2 but now I'm not sure where to go with it? I know I haven't explained my own workings very well, but like I said it's 2am here and I can't really concentrate very well. I really need help, I've been trying to figure out these last 4 questions for a couple days now, the rest of the assignment was easy compared to these.