The ball can't reach the speed of 20 m/s in two seconds, unless you THROW it down from the window with a little bit of initial speed. If you just drop it, then the highest speed it can have after two seconds is 19.6 m/s .
If an object starts from rest and its speed after 2 seconds is 20 m/s, then its acceleration is 20/2 = 10 m/s^2 .
(Gravity on Earth is only 9.8 m/s^2.)
Answer:
You pull on the oars. By the third law, the oars push back on your hands, but that’s irrelevant to the motion of the boat. The other end of each oar (the blade) pushes against the water. By the third law, the water pushes back on the oars, pushing the boat forward.
Answer:
c. about 1/10 as great.
Explanation:
While jumping form a certain height when we bend our knees upon reaching the ground such that the time taken to come to complete rest is increased by 10 times then the impact force gets reduced to one-tenth of the initial value when we would not do so.
This is in accordance with the Newton's second law of motion which states that the rate of change in velocity is directly proportional to the force applied on the body.
Mathematically:
since mass is constant
when 
then,
the body will experience the tenth part of the maximum force.
where:
represents the rate of change in dependent quantity with respect to time
momentum
mass of the person jumping
velocity of the body while hitting the ground.
Answer:
They are known as isotopes
Answer:
C. She should get the Earth spinning on its axis again.
Explanation:
The Earth experiences day and night because of its spinning on its own axis.
If Kara's science-fiction story doesn't have the Earth spinning on its own axis, then the Earth will not experience day and night and hence Kara should incorporate this idea into his story.
