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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 at the start and end of its travel.
The kinetic energies of the block when it is 2m below the start is 250J and the 642 J when it is 2m above the ground.
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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
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So, I showed you how to start the solution and how to promote;
I hope that you will be able to do the rest of the solution on your own.