This is another one of those muddy misleading questions, followed by
a muddy group of choices from which an answer must be selected.
a). is absurd. There's no such thing as a "balanced force", only
a balanced group of forces.
b). is probably the choice the question is aiming for.
c). is not so. The engines of an airplane do plenty of work lifting the plane
off the ground, although the force of the engines is never directed upward.
d). is really awkward. The object's motion is almost never the cause of the force.
The force is almost always the cause of the object's motion.
Now for the big 800-lb gorilla in the room: No moving object needs to be involved
in order for energy to be flowing or work to be getting done.
-- A radio wave radiates through space. Straighten out a wire coat-hanger and
stick it up in the air where the radio wave can pass by it. Electrical current flows
through the wire, and you can drain the electrical energy out the bottom of it.
-- A light bulb is shining. Some distance away, something it's shining on
gets warm, because of the heat energy that has shot across to it from the
light bulb and soaked into it.
-- A lightning bolt jumps from the ground to a passing cloud. Or, if you feel
more comfortable with it, a lightning bolt jumps from a cloud to the ground.
It doesn't matter. Either way, there's enough energy splashing around to
ignite houses, zap TVs and computers, melt concrete, vaporize water, and
light up a city. Although nothing is moving.
It depends on what that "certain amount" is.
<span>The heliocentric model of the
universe was proposed by Nicolaus Copernicus. There are numerous scientist in
ancient times who try to explain what happens in the universe. He may not be
the first one who proposed that what astronomical body is the center of the
universe. However, he stated that the center of the universe was the sun, not
the earth. And the earth revolves around it. It is in his book on the
Revolutions of the Heavenly Bodies. It was only published as he lay in his
deathbed. </span>
Answer:
6.22 N/m
Explanation:
From Hooke's law we deduce that F=kx where F is the applied force and k is the spring constant while x is the extension or compression of the spring. Making k the subject of the above formula then
We also know that the force F is equal to mg where m is the mass of an object and g is acceleration due to gravity hence substituting F with mg we get that
Substituting m with 425 g which is equivalent to 0.425 kg and g with 9.81 then 0.67 for x we get that
Therefore, the spring constant is approximately 6.22 N/m
Displacement/Time = 21m / 15s .
That's choice-D .
