Since force is mass*acceleration,
F = 70kg * 9.8 m/s
Answer:

Explanation:
The momentum change is defined as:

Taking the downward motion as negative and the upward motion as positive, we have:

Replacing (2) and (3) in (1):

Answer:
Yes, Mirror are a surface that reflects light more perfectly than ordinary objects.
Explanation:
Answer:
Concrete
Explanation:
The speed at which sound propagates is medium dependent. As one of the forms of mechanical waves, sound requires a material medium for propagation from place to place.
- Sound travels with the least speed in air because air particles are far apart and they are randomized.
- Sound travels with the greatest speed in solids. Concrete is the only solid material given in the choice.
The speed of sound increases from air to liquid and to solid.
Dna is the way to answer this questions