Potential energy = mass x gravity x height
P.E = 4 x 9.8 x 3
P.E = 117.6 J
The coordinate system should have the origin at the point where the feather is dropped and the downward direction is to be taken as positive.
All falling bodies experience acceleration towards the center of the Earth due to the force of gravitational attraction exerted on the object by the Earth. A feather, when dropped experiences an acceleration in the downward direction. Since the acceleration of the feather is in the downward direction, a feather, when dropped with zero initial velocity, has its velocity vector directed in the direction of its acceleration.
If the downward direction is taken as positive, the falling feather can be said to have a positive velocity and a positive acceleration.
Answer: Government passing regulatory laws
Car emissions testing
Carpooling and less driving overall
Air pollution results when a mixture of particles and gases that can reach in harmful concentrations both outdoors as well as indoors. This increase in concentration can lead to rise in the temperatures and global warming it is also related with the health hazards. Soot, smoke, pollen, carbon dioxide, carbon monoxide and methane are the examples of the common pollutants.
Government passing regulatory laws: The government can ban some of the fossil fuels to prevent air pollution, and some vehicles which are likely to emit more partially combustible gases.
Car emission testing: Nowadays, cars and other vehicles are equipped with catalytic converters which converts the uncombustible gaseous products into less harmful gases which are emitted from the vehicle. The car gas emission testing should be performed to either allow a vehicle or ban the movement of the vehicle.
Carpooling and less driving overall: Carpooling is the sharing of one vehicle with more than one individual. This will prevent the need of others to drive another vehicle. The less the number of vehicles on the road the lesser will be the emission of gases and less pollution will be caused.
Answer: -4.4 m/s
Explanation:
This problem can be solved by the Conservation of Momentum principle, which establishes that the initial momentum 
must be equal to the final momentum 
:
(1)
Where:
(2)
(3)
is the mass of the child
is the initial velocity of the child
is the mass of the adult
is the initial velocity of the adult (it is sitting still)
is the final velocity of the child
is the final velocity of the adult
Substituting (2) and (3) in (1):
(4)
Isolating :
(5)
(6)
Finally:
This means the velocity of the child is in the opposite direction
