Form a hypothesis. Which will be greater, the potential energy of the car at the top of the ramp or the kinetic energy of the ca
1 answer:
The potential energy of the car at the top of the ramp is greater than the kinetic energy of the car at the bottom of the ramp
Explanation:
Here we have a car moving down along a ramp. In absence of force of friction, the total mechanical energy of the car while moving down would be conserved:
where
PE is the potential energy
KE is the kinetic energy
However, this is not true if friction acts on the car. When the car is still at the top of the ramp, its speed is zero, so its kinetic energy is zero, and all the energy is just potential energy:
While the car moves down along the ramp, friction does work on it, and part of the total mechanical energy is wasted and converted into thermal energy. As a result, the car reaches the bottom of the ramp with a final energy which is less than the initial energy:
Also, at the bottom of the ramp, all the energy is just kinetic energy, since the height of the car is now zero, so
It follows that
So, the potential energy of the car at the top of the ramp is greater than the kinetic energy of the car at the bottom of the ramp.
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• <u>According to given question</u> :
<h2>Answer: 0.17</h2>
Explanation:
The Stefan-Boltzmann law establishes that a black body (an ideal body that absorbs or emits all the radiation that incides on it) "emits thermal radiation with a total hemispheric emissive power proportional to the fourth power of its temperature":
(1)
Where:
is the energy radiated by a blackbody radiator per second, per unit area (in Watts). Knowing
is the Stefan-Boltzmann's constant.
is the Surface area of the body
is the effective temperature of the body (its surface absolute temperature) in Kelvin.
However, there is no ideal black body (ideal radiator) although the radiation of stars like our Sun is quite close. So, in the case of this body, we will use the Stefan-Boltzmann law for real radiator bodies:
(2)
Where is the body's emissivity
(the value we want to find)
Isolating from (2):
(3)
Solving:
(4)
Finally:
(5) This is the body's emissivity