The rate of change of d(t) at t = 2 and t = 6 is the ratio between the change of distance (difference between the distances) to the time elapsed. That is,
r = (576 - 64) / (6 - 2) = 128 ft /s
The rate of change is equal to 128 ft/s and this represents the average speed at this time interval.
I believe that the answer to the question provided above is that with increase in resistance provided with constant current, Power dissipated will be lessen since power loss is high. Low power dissipation has low heat production.
Hope my answer would be a great help for you.
Since the table does not accelerate, the upward and downward forces must cancel. Since the downward force of the table legs on the ground is the weight of the table and the book, 175N, this is also the force the pushing up on the table legs by the floor.