Answer:Momentum
Explanation:
Product of an object mass and velocity is called Momentum. Basically momentum is the measure of mass in motion . More is the mass more will be the momentum and similar applies for velocity.
For example a bus moving with low velocity can have a same momentum as that of a bullet moving with a very high velocity
Momentum is denoted by Symbol P

Answer:
(a) The elevator has an acceleration of 2.14 m/s² and direction is downward
(b) The acceleration is a=2.14 m/s²
Explanation:
Let +y be upward direction
For Part (a)
The mass of student (whose weight is 550N) is:
ms=w/g
ms=550/9.8=56.1 kg
Apply ∑Fy=ma

Solve for acceleration a

The elevator has an acceleration of 2.14 m/s² and direction is downward
Part(b)
For the acceleration is the scale reads 670 N
For n=670N
So

An advantage of sustainable energy is that it diversifies the energy supply and reduces importance on imported fuels.
A disadvantage is that all types of gaining access to sustainable energy requires a lot of space/ land. This may prevent important necessities such as housing to not have enough land. Hope this helps ;)