2.0 meters The skateboarder has 2 forces acting upon him to slow him down. The forces are friction, and climbing against the gravitational acceleration. So let's calculate the magnitude of these forces to see how fast he's decelerated. The coefficient of kinetic friction is a multiplier to use against the normal force of the object. We can calculate the normal force by multiplying the mass of the object by the local gravitational acceleration and the cosine of the angle. So Df = 60 kg * 9.8 m/s^2 * cos(20°) * 0.30 Df = 60 kg * 9.8 m/s^2 * 0.939692621 * 0.30 Df = 60 kg * 9.8 m/s^2 * 0.939692621 * 0.30 Df = 165.7617783 kg*m/s^2 Df = 165.7617783 N
The second amount of force is that caused by gravitational acceleration while climbing. That is determine by the amount of height gained for every meter along the slope. We can calculate that using the sine of the angle. So
Dg = 60 kg * 9.8 m/s^2 * sin(20°)
Dg = 60 kg * 9.8 m/s^2 * 0.342020143
Dg = 201.1078443 kg*m/s^2
Dg = 201.1078443 N
So the amount of force decelerating the skateboarder is:
F = Df + Dg
F = 165.7617783 N + 201.1078443 N
F = 366.8696226 N
Now let's determine how much kinetic energy needs to be dissipated. The equation is
E = 0.5 MV^2
So we'll substitute the known values and calculate
E = 0.5 MV^2
E = 0.5* 60 kg * (5 m/s)^2
E = 0.5* 60 kg * 25 m^2/s^2
E = 750 kg*m^2/s^2
E = 750 J
Now let's divide the energy by the force.
750 kg*m^2/s^2 / 366.8696226 kg*m/s^2 = 2.04432298 m
Rounding to 2 significant figures gives a distance of 2.0 meters.
<h2>Answer: Venus</h2>
Galileo was the first to use the telescope to observe the heavens, mainly observing the Moon, the Sun with its sunspots, Jupiter with its moons and Venus (in the early 1600s).
In the case of Venus, he observed that it presented phases (such as those of the moon) together with a variation in size; observations that are only compatible with the fact that Venus rotates around the Sun and not around Earth.
This is because Venus presented its smaller size when it is in full phase and the largest size when it is in the new one, when it is between the Sun and the Earth.
These images along with other discoveries were presented to the Catholic Church (which supported the <u>geocentric theory</u> for that time) as a proof that completely refutes Ptolemy's geocentric system and affirms <u>Copernicus' heliocentric theory.</u>
NATURAL MAGNETS
A natural magnet is one that occurs naturally in nature. All natural magnet are permanent magnets , meaning they never lose their magnetic power.
Natural magnet can be found in Sandy deposits in various part of the earth .
The strongest natural magnetic material is LODESTONE also called magnetite.
ARTIFICIAL MAGNETS
These are magnets made by people.
It's these magnets that is in our refrigerator doors, which have extra-stronge magnetic power. There are two types of of artificial magnets. Temporary and Permanent Magnets.
Examples of artificial magnets are; electromagnet and the paper clip.
Examples of Permanent Magnets are; Alnico
Answer:
The time taken for the light to travel from the earth to the sun = 496.67 seconds
Explanation:
Estimated distance of the earth to the sun = 149000000km
Speed of light = 300000km/s
Time taken for the light to travel from the sun to the earth = ?
Speed = Distance/time
time = Distance/speed
time = 149000000/300000
time = 496.67 s
The time taken for the light to travel from the earth to the sun = 496.67 seconds
The first attempt was made in 1957
