(a) 154.5 N
Let's divide the motion of the sprinter in two parts:
- In the first part, he starts with velocity u = 0 and accelerates with constant acceleration for a total time During this part of the motion, he covers a distance equal to , until he finally reaches a velocity of . We can use the following suvat equation:
which reduces to
(1)
since u = 0.
- In the second part, he continues with constant speed , covering a distance of in a time . This part of the motion is a uniform motion, so we can use the equation
(2)
We also know that the total time is 10.0 s, so
Therefore substituting into the 2nd equation
From eq.(1) we find
(3)
And substituting into (2)
Solving for t,
So from (3) we find the acceleration in the first phase:
And so the average force exerted on the sprinter is
b) 14.5 m/s
The speed of the sprinter remains constant during the last 55 m of motion, so we can just use the suvat equation
where we have
u = 0
is the acceleration
is the time of the first part
Solving the equation,
The kinetic energy is .
Explanation:
The kinetic energy of an object is given by
where
K is the kinetic energy of the object
m is the mass of the object
v is the speed of the object
For the comet in this problem, we have:
is its mass
is the speed
First, we convert the speed from km/h to m/s:
Therefore, the kinetic energy of the comet is
Learn more about kinetic energy here:
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<h2>
Answer: B)Scientists’ understanding of cells continually improved as the results of studies built upon each other over time and formed the cell theory.</h2>
Explanation:
Nowadays we know <u>cells are essential microscopic units that make up the living beings, capable of reproducing independently. </u>
However, this is the result of a long process of discoveries and studies made since the 19th century, in which the continuous improvement of new technologies was helpful.
In fact, it is wel known the English scientist Robert Hooke was the first to discover the existence of cells by looking through a compound microscope at a cork sheet, realizing that it was made up of small polygonal holes (like those of a honeycomb) that reminded him of the chambers in which the monks stayed (called cells). Then, during the next centuries more studies were made until we had the current knowledge about the structure of a cell.