A 30-N stone is dropped from a height of 10 m and strikes the ground with a speed of 13 m/s.
What average force of air friction acted on the stone as it fell?

4.1 N

Step-by-step explanation:

We can solve this problem by using considerations about energy.

At the moment the stone is dropped, it has only gravitational potential energy:

where

is the weight of the stone

h = 10 m is the initial height of the stone

As the stone falls, part of this energy is converted into kinetic energy, while part into thermal energy due to the presence of the air friction, acting opposite to the motion of the stone:

where:

is the mass

v = 13 m/s is the final speed of the stone

is the thermal energy

The thermal energy is actually equal to the work done by the air friction on the stone:

where

F is the average force of friction

h = 10 m

Since the total energy must be conserved, we can combine the three equations, so we find:

And solving for F, we find the average force of air friction:

there are 70 more legs than eyes at the dog show (196 – 126 = 70). dogs have two more legs than eyes, and humans have the same number of legs as eyes. thus 70 is twice the number of dogs at the show, so the number of dogs is half of 70, which is 35. to get the number of humans, subtract 35 from 63: 63 – 35 = 28.

step-by-step explanation:

nope.   happens to me as well.

-aparri