Estimate frequency of vibration of your arm. let the length of the arm be 0.57 m. consider the arm as a simple pendulum and assume its center of mass is about 2/3 its length from the shoulder. express your answer with the appropriate units. estimate the natural period of vibration of your arm.

Keneila is attempting to ski down a 20 m high friction free hill for the first time. she has a speed 10 m/s at the top. what is her kinetic energy when she is a the bottom, 20 m ? (a)2500 j (b)9800 j (c)12300 j (d)3100j (e)15000j

Will you chech and finish these for me, because i am stumped with them.

When a vertical beam of light passes through a transparent medium, the rate at which its intensity i decreases is proportional to i(t), where t represents the thickness of the medium (in feet). in clear seawater, the intensity 3 feet below the surface is 25% of the initial intensity i0 of the incident beam. what is the intensity of the beam "10" feet below the surface? (give your answer in terms of i0. round any constants or coefficients to five decimal places.)