A 45 kg swimmer starting from rest can develop a maximum speed of 12 m/s over a distance of 20 m. How much net force must be applied to do this?

What defines the mass number of an isotope? a. the sum of the neutrons and protons b. the sum of the neutrons and electrons c. the number of neutrons d. the number of protons

Consider a double atwood machine constructed as follows: a mass 4m is suspended from a string that passes over a massless pulley on frictionless bearings. the other end of this string supports a second similar pulley, over which passes a second string supporting a mass of 3m at one end and m at the other. using two suitable generalized coordinates, set up the lagrangian and use the lagrange equations to find the acceleration of the mass 4m when the system is released. explain why the top pulley rotates even though it carries equal weights on each side.

Farmer a has a deep well and needs a lot of water for her animals and crops. her neighbor, farmer b, has a shallower well. he needs less water than farmer a because his farm is smaller. in years of drought, sometimes farmer b can't get any water from his wells. what can farmer b do to decrease the likelihood of his well running dry?