SOLUTION: A block of mass m is thrown vertically down form a height of 8.0 meters. Determine the mass of the block, its initial and final velocities, and the potential and kinetic energies a

The change of kinetic energy between the levels of 2 meters below the start and 2 meters above the ground is

    delta_kinetic_energy = 642 - 250 = 392 joules.


This difference is nothing else as the work done by the gravity force, so we can write

    392 = m*g*4 = m*9.81*4.


From this equation, we get the mass of the block  

    m =  = 10 kg    (rounded).       ANSWER


Here 4 meters is the height difference between the referred levels (2 meters below the start and 2 meters above the ground).


The mass is the major unknown in the problem and we just found it out.



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    |    Answering the rest of questions is straightforward calculations.  |
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To find the initial velocity, use the formula for kinetic energy at the level of 2 meters below the start


     250 = mg*2 + ,     

or

    250 = 10*9.81*2 + ,


which gives


    250 - 10*9.81*2 = 

     =  = 10.76 

     =  = 3.28 m/s.      ANSWER