Arock is dropped from the top of a vertical cliff and takes 3.00 s to reach the ground below the cliff. a second rock is thrown vertically from the cliff, and it takes this rock 2.00 s to reach the ground below the cliff from the time it is released. with what velocity was the second rock thrown, assuming no air resistance?
a) 12.3 m/s upward
b) 4.76 m/s downward
c) 4.76 m/s upward
d) 12.3 m/s downward
e) 5.51 m/s downward

The us government wants to allocate billions of dollars in the next 10 years to assure our future energy security. the funds will be spread among a variety of possible energy resources. where do you think the government should put the greatest support: solar energy, wind energy, clean coal, oil exploration, gas exploration, or a combination of sources? are there other efforts that should be explored? support your position with cited information for both questions.

As you are trying to move a heavy box of mass m, you realize that it is too heavy for you to lift by yourself. there is no one around to , so you attach an ideal pulley to the box and a massless rope to the ceiling, which you wrap around the pulley. you pull up on the rope to lift the box. use g for the magnitude of the acceleration due to gravity and neglect friction forces. once you have pulled hard enough to start the box moving upward, what is the magnitude f of the upward force you must apply to the rope to start raising the box with constant velocity? express the magnitude of the force in terms of m, the mass of the box.

Using the free-body diagram, calculate the net force acting on the sled. is the sled in a state of dynamic equilibrium?