Question

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.

Answer 1

Step-by-step explanation:

According to the given situation,

Change in kinetic energy = work done by all the forces

So, Change in kinetic energy = work done by gravitational force + work done by air resistance

`mgh - F_(a)h = (1)/(2)m(v^(2) - 0^(2))`

Initial velocity of the rock will be zero. Since, the gravitational force is in the downwards direction hence, it will be positive. And, force due to air resistance is negative as it is in the upward direction.

Hence, putting the given values into the above formula as follows.

`mgh - F_(a)h = (1)/(2)m(v^(2) - 0^(2))`

`10 * 9.8 * 60 = (1)/(2) * mv^(2)`

K.E = 4086 J

Thus, we can conclude that the K.E at the bottom of the fall is 4086 J.