Which of these statements best explains why it is difficult to see outside at night?
2 answers:
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Answer: 4
The mechanical advantage is the ratio of the force exerted by the object to the force applied to do work on it.
Here, Jeff tried to lift a rock weighing 600 pounds by wedging board under the rock. Jeff who weighs 150 pounds uses all his weight to exert force on lever and lift rock.
Mechanical advantage,
Therefore, the mechanical advantage that lever provided to Jeff in lifting rock is 4.
Answer:
The final velocity of the thrower is and the final velocity of the catcher is
.
Explanation:
Given:
The mass of the thrower, .
The mass of the catcher, .
The mass of the ball, .
Initial velocity of the thrower,
Final velocity of the ball,
Initial velocity of the catcher,
Consider that the final velocity of the thrower is . From the conservation of momentum,
Consider that the final velocity of the catcher is . From the conservation of momentum,
Thus, the final velocity of thrower is and that for the catcher is
.
Answer:
E) are almost circular, with low eccentricities.
Explanation:
Kepler's laws establish that:
All the planets revolve around the Sun in an elliptic orbit, with the Sun in one of the focus (Kepler's first law).
A planet describes equal areas in equal times (Kepler's second law).
The square of the period of a planet will be proportional to the cube of the semi-major axis of its orbit (Kepler's third law).
Where T is the period of revolution and a is the semi-major axis.
Planets orbit around the Sun in an ellipse with the Sun in one of the focus. Because of that, it is not possible to the Sun to be at the center of the orbit, as the statement on option "C" says.
However, those orbits have low eccentricities (remember that an eccentricity = 0 corresponds to a circle)
In some moments of their orbit, planets will be closer to the Sun (known as perihelion). According with Kepler's second law to complete the same area in the same time, they have to speed up at their perihelion and slow down at their aphelion (point farther from the Sun in their orbit).
Therefore, option A and B can not be true.
In the celestial sphere, the path that the Sun moves in a period of a year is called ecliptic, and planets pass very closely to that path.