Rebecca jogs in place for two minutes before her track meet. Rebecca weighs 100 pounds. Which of the following statements is tru
2 answers:
Answer:
B. Rebecca has not done work because she has not moved a distance.
Explanation:
In physics, work represents the amount of energy necessary for a force to move a body a certain distance.
, where <em>F</em> is the force, <em>d</em> the distance and <em>W</em> the work of the force <em>F.</em>
Since Rebecca jogs in place, the distance is zero, an so does the work.
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(a)
The total mechanical energy of the space probe must be constant, so we can write:
(1)
where
is the kinetic energy at the surface, when the probe is launched
is the gravitational potential energy at the surface
is the final kinetic energy of the probe
is the final gravitational potential energy
Here we have
at the surface, (radius of the planet),
(mass of the planet) and m=10 kg (mass of the probe), so the initial gravitational potential energy is
At the final point, the distance of the probe from the centre of Zero is
so the final potential energy is
So now we can use eq.(1) to find the final kinetic energy:
(b)
The probe reaches a maximum distance of
which means that at that point, the kinetic energy is zero: (the probe speed has become zero):
At that point, the gravitational potential energy is
So now we can use eq.(1) to find the initial kinetic energy: