Complete question is;
When you ride a bicycle, in what direction is the angular velocity of the wheels? A) to your left B) to your right C) forwards D) backwards
Answer:
Option A - to your left
Explanation:
While an object rotates, each particle will have a different velocity:
the 'Speed' component will vary with radius while the 'Direction' component will vary with angle.
All of the velocity vectors are aligned in the same plane.
We can be solve this by choosing a single vector normal to ALL of the possible velocity vectors of the rotating object in that plane.
This convention used is known as "Right-hand rule". The angular velocity vector points along the wheel's axle. For instance, if you Imagine wrapping your right hand around the axle so that your fingers point in the direction of rotation, with your thumb sticking out. You will notice that your thumb points to the left.
Thus;
By right-hand rule, a wheel rotating on a forward - moving bicycle has an angular velocity vector pointing to the rider's left.
So, option A is the correct answer
Answer:
i) the minimum acceleration to take off is 22500 km/h²
ii) the required time needed by the plane from starting to takeoff is 0.0133 hrs
iii) required force that the engine must exert to attain acceleration is 625 kN
Explanation:
Given the data in the question;
mass of plane m = 360,000 kg
take of speed v = 300 km/hr = 83.33 m/s
i)
What should be the minimum acceleration to take off if the length of the runway is 2.00 km
from Newton's equation of motion;
v² = u² + 2as
we know that a plane starts from rest, so; u = 0
given that distance S = 2 km
we substitute
(300)² = 0² + ( 2 × a × 2 )
90000 = 4 × a
a = 90000 / 4
a = 22500 km/h²
Therefore, the minimum acceleration to take off is 22500 km/h²
ii) At this acceleration, how much time would the plane need from starting to takeoff.
from Newton's equation of motion;
v = u + at
we substitute
300 = 0 + 22500 × t
t = 300 / 22500
t = 0.0133 hrs
Therefore, the required time needed by the plane from starting to takeoff is 0.0133 hrs
iii) What force must the engines exert to attain this acceleration
we know that;
F = ma
acceleration a = 22500 km/hr² = 1.736 m/s²
so we substitute
F = 360,000 kg × 1.736 m/s²
F = 624960 N
F = 625 kN
Therefore, required force that the engine must exert to attain acceleration is 625 kN
Given:
The frequency of the pendulum ( f) = 0.25 Hz.
Total time (t) = 10 s
Concept: Frequency means, the number of oscillation in one second.
Time period is the required time by pendulum to complete one oscillation.
∵ In 1.0 second, number of oscillations = 0.25
∴ In 10.0 second, number of oscillations = (0.25 ×10.0) / 1.0 = 2.5
Hence, the required number of oscillation = 2.5
Mercury looks pretty, in its shiny, fast-moving liquid form, but don't touch! It can be extremely poisonous to humans.
The symbol Hg that mercury is known by comes from its Greek name, hydrargyrum, which means "liquid silver" — to reflect its shiny surface. The element is also known as quicksilver for its mobility. Named after the fastest-moving planet in the solar system, mercury has been known to humanity for ages. In fact, evidence of its use has been found in China, India and Egypt, and traces of mercury were found in 3,500-year-old Egyptian tombs.
Mercury is a very toxic element. It can enter the body through an open wound or by inhaling or ingesting it. It can then cause damage to nerves, the liver and the kidney, as well as a number of other symptoms.
Despite its toxic qualities, mercury can still be useful to us. The element conducts electricity and is used in electrical switches of thermostats and certain types of doze alarm-type alarm clocks, according to the College of Natural Resources at the University of California, Berkeley (CNR) "The place where people probably see it most commonly is in the new light bulbs — the compact fluorescent light bulbs," where mercury vapor is one of the chemicals used, said Daniel King, an associate professor of chemistry at Drexel University.
Due to its high density and compactness, mercury is also used to make thermometers, barometers and other scientific instruments, according to the Jefferson Lab. However, for safety reasons, consumer use of mercury in thermometers has become less common over the years, as digital thermometers have been introduced. In 2008, 13 states introduced laws that limit the manufacture, sale and/or distribution of mercury fever thermometers: California, Connecticut, Illinois, Indiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Hampshire, Rhode Island, Oregon, Washington, the Environmental Protection Agency reports.
Just the facts
Atomic number (number of protons in the nucleus): 80
Atomic symbol (on the Periodic Table of Elements): Hg
Atomic weight (average mass of the atom): 200.59
Density: 13.5336 grams per cubic centimeter
Phase at room temperature: Liquid
Melting point: minus 37.8 degrees Fahrenheit (minus 38.83 degrees Celsius)
Boiling point: 674.11 F (356.73 C)
Number of isotopes (atoms of the same element with a different number of neutrons): 34. Number of stable isotopes: 7
Most common isotope: 202Hg (29.9 percent natural abundance)
Mercury is typically found in the form of its common ore cinnabar — mercury sulfite — and can rarely be found on its own. To extract pure mercury, the ore is ground up and heated to the temperature of about 1,076 degrees F (580 degrees Celsius) with oxygen present in the process. Mercury vapor escapes from the ores and sulfur dioxide is removed, according to CNR. The metal is condensed and washed with nitric acid to purify it, and then distilled.
Mercury can form alloys with gold, silver, zinc and cadmium, which are called amalgams. Through those amalgams, mercury can be used to extract gold from rocks. When mercury comes into contact with gold, the gold dissolves into the mercury and then the two are separated, with the mercury being distilled off.
Mercury also forms compounds with other elements. Interestingly, one of such compounds — mercury nitrate — played a role in the coining of the term "mad as a hatter."
"Mercury was actually used in the making of hats from animal pelts," King said. In the 18th century people used the mercury nitrate compound to clean the pelts before they turned them into hats.
"And they discovered that a large percentage of the people who were working with those chemicals ended up suffering from brain damage," he said. "So the term 'mad as a hatter' actually comes from exposure to mercury."
