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Answer:
<em>The required constant friction force for the last 20 m is 6,862.8 N</em>
Explanation:
<u>Energy Conversion</u>
There are several ways the energy is manifested in our physical reality. Some examples are Kinetic, Elastic, Chemical, Electric, Potential, Thermal, Mechanical, just to mention some.
The energy can be converted from one form to another by changing the conditions the objects behave. The question at hand states some types of energy that properly managed, will make the situation keep under control.
Originally, the m=220 kg car is at (near) rest at the top of a h=101 m tall track. We can assume the only energy present at that moment is the potential gravitational energy:
For the next x1=230 m, a constant friction force Fr1=350 N is applied until it reaches ground level. This means all the potential gravitational energy was converted to speed (kinetic energy K1) and friction (thermal energy W1). Thus
We can compute the thermal energy lost during this part of the motion by using the constant friction force and the distance traveled:
This means that the kinetic energy that remains when the car reaches ground level is
We could calculate the speed at that point but it's not required or necessary. That kinetic energy is what keeps the car moving to its last section of x2=20 m where a final friction force Fr2 will be applied to completely stop it. This means all the kinetic energy will be converted to thermal energy:
Solving for Fr2
The required constant friction force for the last 20 m is 6,862.8 N