A dolphin can swim at a constant speed of 12.5 m/s. How
2 answers:
Answer:
Explanation:
Time can be found by dividing the distance by the speed.
The distance is 45 meters and the speed is 12.5 meters per second.
Divide. Note that the meters, or "m" will cancel each other out.
It will take the dolphin 3.6 seconds to swim a distance of 45 meters are 12.5 meters per second.
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where
is the mass, 
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Putting the numbers in, we find the potential energy
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where v is the speed of the rock just before hitting the ground. Since the mechanical energy of the rock must be conserved, then the kinetic energy K before hitting the ground must be equal to the initial potential energy U of the rock:
3) For the work-energy theorem, the work W done by the gravitational force on the rock is equal to the variation of kinetic energy of the rock, which is:
where U is the gravitational potential energy and K the kinetic energy.
Initially, the kinetic energy is zero (because the rock starts from rest, so its speed is zero), and the total mechanical energy of the rock is just gravitational potential energy. This is equal to
where
Putting the numbers in, we find the potential energy
2) Just before hitting the ground, the potential energy U is zero (because now h=0), and all the potential energy of the rock converted into kinetic energy, which is equal to:
where v is the speed of the rock just before hitting the ground. Since the mechanical energy of the rock must be conserved, then the kinetic energy K before hitting the ground must be equal to the initial potential energy U of the rock:
3) For the work-energy theorem, the work W done by the gravitational force on the rock is equal to the variation of kinetic energy of the rock, which is: