A 10 kg rock that has been dropped from a 60 meter high cliff experiences a average force of air resistance of 30 N. Calculate the KE at the bottom of the fall.
so KE=PEgravity 5880 is the PE but no friction force deducted...do I just subtract 30N?
my book is not clear...
KE at bottom=PE at top - friction=PE at top - forcefriction*height
so 60 x 30
5880-1800=4080
To calculate the kinetic energy (KE) at the bottom of the fall, we need to subtract the average force of air resistance (friction force) from the potential energy due to gravity (PEgravity).
PEgravity is given by the formula: PEgravity = mgh, where m is the mass of the object (10 kg), g is the acceleration due to gravity (9.8 m/s^2), and h is the height of the cliff (60 m).
So, PEgravity = (10 kg) * (9.8 m/s^2) * (60 m) = 5880 J
Now, we need to subtract the average force of air resistance (30 N) from PEgravity to find KE at the bottom of the fall:
KE = PEgravity - Friction force
KE = 5880 J - 30 N
However, in order to subtract the friction force from the potential energy, we need to express both quantities in the same units.
The unit of energy (Joules) and the unit of force (Newton) are not directly compatible. In order to make them compatible, we need to multiply the friction force (30 N) by the distance over which it acts. This distance is not provided in the question, so we cannot directly subtract the friction force.
If you are given the distance over which the friction force acts, you can calculate the work done by the friction force and subtract it from the potential energy to find the kinetic energy. The work done by a force is given by the formula Work = Force * Distance, where the distance is the distance traveled in the direction of the force.
However, since the question does not provide the distance over which the friction force acts, we cannot calculate the kinetic energy at the bottom of the fall accurately.
In summary, to calculate the kinetic energy at the bottom of the fall, we need to know the distance over which the friction force acts, in addition to the mass of the object, the height of the cliff, and the average force of air resistance.