On Earth, gravity increases the speed of a falling object by about 9.8 m/s
every second that it falls.
In 0.4 second, its speed increases by (0.4 x 9.8) = 3.92 m/s.
If it just rolled off of the shelf at the beginning of that 0.4 second, then it
started from zero speed, and its speed after 0.4 second is 3.92 m/s.
Its velocity is 3.92 m/s downward.
For #2.
(A) The resultant velocity of the boat is the hypotenuse of a right triangle with the sides being the river and boat velocities.
The Pythagorean theorem: h^2 = a^2 + b^2
then you can use: soh cah toa to find any angles.
(B) The river velocity is not opposing the direction of travel, it increases the boats velocity from 2m/s to 2.5m/s
Refraction is caused by any wave crossing the boundary out of one substance and into another one. The two different substances may be no more than two parcels of air at different temperatures.
Answer:
The element "AI" has:
Protons: 13 Neutrons: 14 Electrons: 13
Have a great day.
