The law says things travel in a straight line at constant speed unless acted upon by a force. But friction is a force but it can't be seen easily other than its effect, which is to bring the object to rest in seeming violation of the 1st law.
We have: Gravitational Potential Energy (U) = mgh
Here, m = 3 Kg
g = 9.8 m/s² [ constant value for earth system ]
h = 3 m
Substitute their values into the expression:
U = 3 × 9.8 × 3
U = 88.2 J
In short, Your Answer would be 88.2 Joules
B) The amount of work done
Hello:
The pivot point of a LEVER is called the fulcrum.
Answer:
So airplane will be 1324.9453 m apart after 2.9 hour
Explanation:
So if we draw the vectors of a 2d graph we see that the difference in angles is = 83 - 44.3 = 
Distance traveled by first plane = 730×2.9 = 2117 m
And distance traveled by second plane = 590×2.9 = 1711 m
We represent these distances as two sides of the triangle, and the distance between the planes as the side opposing the angle 38.7.
Using the law of cosine, 
representing the distance between the planes, we see that:
d = 1324.9453 m
