Clouds absorb outgoing radiation emitted by earth and reradiate a portion of it back to the surface during _____.
1 answer:
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Answer:
B) A stack of books is carried at waist level across a room
Explanation:
Work is defined as:
where
F is the force applied
d is the displacement of the object
is the angle between the direction of the force and of the displacement
From the formula, we see that the work done is zero when the force and the displacement are perpendicular to each other. Let's now analyze each situation:
A) A bookcase is slid across carpeting. --> work is done, because the force that pushes the bookcase is in the same direction of the displacement
B) A stack of books is carried at waist level across a room. --> no work is done, because the force to carry the book is vertical, while the displacement of the books is horizontal
C) A chair is lifted vertically with respect to the floor. --> work is done, because the force that lifts the chair is vertical, and the displacement is vertical as well
D) A table is dropped onto the ground. --> work is done, because the force of gravity (that makes the table falling down) is vertical and the displacement of the table is also vertical.
Answer:
<em>The second ball has four times as much kinetic energy as the first ball.</em>
Explanation:
<u>Kinetic Energy </u>
Is the type of energy an object has due to its state of motion. It's proportional to the square of the speed.
The equation for the kinetic energy is:
Where:
m = mass of the object
v = speed at which the object moves
The kinetic energy is expressed in Joules (J)
Two tennis balls have the same mass m and are served at speeds v1=30 m/s and v2=60 m/s.
The kinetic energy of the first ball is:
The kinetic energy of the second ball is:
Being m the same for both balls, the second ball has more kinetic energy than the first ball.
To find out how much, we find the ratio:
Simplifying:
The second ball has four times as much kinetic energy as the first ball.