Ah jeeze, I am so sorry to be posting up three questions. I don't mean to just get answers for my homework, but would anybody be willing to lead me in the right direction regarding these physics problems? I have the solutions, but I am unsure on how to get them. Thank you, anything helps.(adsbygoogle = window.adsbygoogle || []).push({});

1) A solid sphere with a mass of 4.0 kg and a radius of 0.12 m starts from rest at the top of a ramp inclined at 15 degrees and rolls to the bottom. The upper end of the ramp is 1.2 m higher than the lower end. What is the total kinetic eneergy of the sphere when it reaches the bottom? (Assume that the sphere rolls without slipping and that g=9.81 m/s/s.)

--- When I first attempted this problem, I used KE(tot)=KE(rot) + KE(trans) to set things up, but I don't have the angular velocity, nor the acceleration/time.

--- The answer is 47 J

2) A 4.0 m board with a mass of 19 kg is pivoted at its center of gravity. A helium balloon attached 0.23 m from the left end of the board produces an upward force of 7.0 N. A 2.5 kg book is placed 0.73 m from the left end of the board, and another book of 1.3 kg is placed 0.75 m from the right end of the board. Find the torque on the board and the direction of rotation.

--- This problem is a very wordy one. I have my diagram drawn and everything. My first approach was to calculate torque for each side, seeing as it should be balanced (then net torque is zero). However, I ran into problems when calculating it because of the varying distances and masses (ie, what is the distance I use to calculate torque, do I configure in the board's mass, if so, how?)

--- The answer is 15 N*m

3) A force of 1250 N is needed to move a crate weighing 3270 N up a ramp that is 4.55 m long. If the elevated end of the ramp is 0.750 m high, what is the efficenicy of the ramp?

--- This problem seemed easy, but when I checked my answer, I was wrong. At frist I though I could just divide the to work output and work input, but I did not end up with the right answer, yet again. What confuses me the most, though, is when it says the crate weights #. How do I confiigure in the weight, along with the force required and distance?

--- The answer is 43.1%

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# Homework Help: Rotational Equilibrium and Dynamics

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