Questions posted in Physics

A substance can be classified by its physical properties which are properties that

Physical properties are properties that you can see, feel and measure, they do not change the matter of the substance. Some examples of physical properties are Mass, Color, Shape, Hardness and Boiling point.

ANSWERED AT 06/12/2019 - 03:05 PM

QUESTION POSTED AT 06/12/2019 - 03:05 PM

How much time would it take for an airplane to reach its destination. If it traveled at an average velocity of 790km/hr east for a distance of 4,700 kilometres

It would be 5.94 hours but you can round it to just 6 hours.

ANSWERED AT 06/12/2019 - 03:01 PM

QUESTION POSTED AT 06/12/2019 - 03:01 PM

What evidence did Alfred Wegener use to support his theory of continental drift?


Alfred Wegener was a meteorologist and geologist. He was inspired by a map of continents to start the journey of explaining Earth's geological history. He gave the theory of continental drift which says that the continents of Earth have moved relative to each other over time. He used following evidences to support his theory:

1. The facing side of South America's and Africa's shoreline interlocks perfectly. Which implies they must have been joined together in history.

2. Fossil of same type of reptiles found on different continents separated by huge oceans.

3. Matching the rock pieces on either side of the Atlantic oceans.

ANSWERED AT 06/12/2019 - 02:56 PM

QUESTION POSTED AT 06/12/2019 - 02:56 PM

A 20 kg crate of books is at rest on a table. what is the normal force on the books?

The weight of 20 kg is

                             (mass) x (gravity) =

                                   (20 x 9.8) = 196 newtons, downward.

There must be a force of 196 newtons upward on the mass. 
Otherwise the mass is accelerating either up or down.

ANSWERED AT 06/12/2019 - 02:54 PM

QUESTION POSTED AT 06/12/2019 - 02:54 PM

Greyhounds can accelerate at 7 m/s2 at the start of a race. How much force does it take a 35 kg dog to produce this acceleration

Force = (mass) x (acceleration)              Newton's second law of motion.

Force = (35 kg) x (7 m/s²)  =  245 newtons

                                    (about  55 pounds)

ANSWERED AT 06/12/2019 - 02:54 PM

QUESTION POSTED AT 06/12/2019 - 02:54 PM

Which phrase describes an atom?

You haven't included the list of choices that goes with the question, so it's
impossible for me to choose the correct one, or to help you choose it.

Regarding my ability to answer the question and collect the 5-point bounty,
I'm free to make up any phrase of my own that correctly describes an atom.

-- very very very very very very very tiny

-- includes even tinier particles, with electric charges
   both positive and negative

-- smaller than the wavelength of visible light

ANSWERED AT 06/12/2019 - 02:45 PM

QUESTION POSTED AT 06/12/2019 - 02:45 PM

If you wanted to detect x-rays coming from the sun, where would you place the detector? And why?

The Sun does emit xrays. You'd have to place your sensor above the Earth's atmosphere because it blocks out nearly all x-rays. This is why we have the Chandra observatory ( )

ANSWERED AT 06/12/2019 - 02:45 PM

QUESTION POSTED AT 06/12/2019 - 02:45 PM

A bus slams on its breaks and goes from 30 km/hr to 15km/hr in 4 seconds. What is its acceleration?

Acceleration = (change in speed) / (time for the change).

Change in speed = (15 - 30) = -15 km/hr
Time for the change = 4 sec

Acceleration = (-15 km/hr) / (4 sec) = -3.75 km/hr per second .

Is that a lot ?  Not much ?

Let's convert it to a unit that we can think about:

     (-15 km/hr) x (1,000 m/km) x (1 hr / 3,600 sec) =

           (-15 x 1,000) / (3,600)  =  -(4 and 1/6) m/sec .

So the acceleration of the bus is    -(4 and 1/6) m/sec² .

The negative sign means that it slowed down.

(4 and 1/6) m/sec²  is about  42%  of the acceleration of gravity ...
the acceleration the bus would have if it drove off of a cliff.

When the car or the bus you're riding in slows down at that rate,
you feel  42%  of your weight pulling you forward against your
seat belt.  That's quite a drastic acceleration !

ANSWERED AT 06/12/2019 - 02:36 PM

QUESTION POSTED AT 06/12/2019 - 02:36 PM

Every 4 years we have a leap year on our calander to make up the extra.......

The Earth takes very nearly (365 and 1/4) days to go around the sun.

If our calendar always had 365 days, then the year would end and re-start
too soon, and the beginning of Spring (and every other season) would
eventually drift into the months after March.

If our calendar always had 366 days, then the year would end and re-start
too late, and the beginning of Spring (and every other season) would
eventually drift into the months before March.

We can't make calendars with an extra quarter-day in each year.  But we
keep them lined up with the real year by saving up the quarters, and adding
one full day to the calendar every 4 years.

ANSWERED AT 06/12/2019 - 02:35 PM

QUESTION POSTED AT 06/12/2019 - 02:35 PM

People in the United States know that water boils at 212°F. In Europe, people know that water boils at 100°C. Is the water in the U.S. different than the water in Europe? What explains the two different temperatures?

They are not two different temperatures.  They are two different
descriptions of the same temperature, using different-size degrees
and different scales.  A lot like "60 miles per hour" and "96.6 kilometers
per hour" ... the same speed. 

In the case of the temperatures, the tags " °F " and " °C " show that the
units are different.  And even though it's not obvious from the descriptions,
they also start counting at different temperatures.

ANSWERED AT 06/12/2019 - 02:33 PM

QUESTION POSTED AT 06/12/2019 - 02:33 PM

A complete series circuit consists of a 12.0 V battery, a 4.70 O resistor, and a switch. The internal resistance of the battery is 0.30 O. The switch is open. What does an ideal voltmeter read when placed across the terminals of the switch? 12.0 V 9.40 V 2.40 V zero

With the switch open, there's no current in the circuit, and therefore
no voltage drop across any of the dissipative elements (the resistor
or the battery's internal impedance).  So the entire battery voltage
appears across the switch, and the voltmeter reads 12.0V .

ANSWERED AT 06/12/2019 - 02:14 PM

QUESTION POSTED AT 06/12/2019 - 02:14 PM

In order for a color to be seen by a human, the light must be what?

The light must be within a certain, rather narrow, range
of wavelength/frequency, and it must enter his eye.

ANSWERED AT 06/12/2019 - 02:05 PM

QUESTION POSTED AT 06/12/2019 - 02:05 PM

On a high way a car is driven 80 km the first 1 he of travel, 50km during the next 0.5 he, and 40 km in the final 0.5 hr. What is the cars average speed for the entire trip?

Average speed = (total distance covered) / (total time to cover the distance) .

Total distance = (80 + 50 + 40) = 170 km

Total time = (1 + 0.5 + 0.5) = 2 hours

Average speed = (170 km) / (2 hrs) = 85 km/hr .

ANSWERED AT 06/12/2019 - 02:03 PM

QUESTION POSTED AT 06/12/2019 - 02:03 PM

Stable system where forces cancel eachother out

Equilibrium - stable system where forces cancel each other out

ANSWERED AT 06/12/2019 - 01:54 PM

QUESTION POSTED AT 06/12/2019 - 01:54 PM

Why do ice cubes always float at the top of a glass of water?

Because water is a very very very very very unusual substance ... It's
the only known substance whose solid form is less dense than its liquid
form near the same temperature.

In other words, water is the only known substance for which a solid lump
of it floats in a liquid glass of it.

If that were not true ... if the behavior of the density of water around its
freezing temperature were the same as the density of all other known
substances ... then life on Earth would be impossible.

Think about that for a while !  Ya gotta admire whoever it was that designed water !

ANSWERED AT 06/12/2019 - 01:51 PM

QUESTION POSTED AT 06/12/2019 - 01:51 PM

Give an example of a situation in which you would describe an object's position in one dimension two dimensions three dimension

One dimension:

I'm waiting patiently for the elevator.  What floor is it on now ?

Two dimensions:
What's the address of your house ?
Where do you want this picture hung on your bedroom wall ?
Where is the Maersk Skokie supertanker located today ?
Where are your rooks and pawns on the chessboard ?

Three dimensions:
I'm waiting at the airport for my brother to arrive.
He's on Flight AC3715.
Where is the flight located right now ?

ANSWERED AT 06/12/2019 - 01:43 PM

QUESTION POSTED AT 06/12/2019 - 01:43 PM

A SI unit used to measure force, equal to less than one-quarter of a pound, is the what

The SI unit of force is the Newton.

1 newton is the force that accelerates a 1 kilogram mass
at the rate of 1 meter per second².

1 pound of force is equivalent to roughly  4.448 newtons.

(1 newton is equivalent to roughly  0.225  pounds of force.)

ANSWERED AT 06/12/2019 - 01:33 PM

QUESTION POSTED AT 06/12/2019 - 01:33 PM

Does a stick of dynamite contain force?

No.  Force isn't something you can enclose in a box, an envelope,
or a bottle.

A stick of dynamite contains some amount of a chemical compound which,
when triggered by enough heat or shock, undergoes a chemical reaction
that proceeds very rapidly, and generates a large quantity of gases before
the gases can dissipate.  This creates very high pressure around the reaction,
and it's this pressure in a small volume that exerts great force for a very short
time.     The whole process is often described as an "explosion".

ANSWERED AT 06/12/2019 - 01:32 PM

QUESTION POSTED AT 06/12/2019 - 01:32 PM

How are the relationships of elements in a group different from the relationships of elements in a period?

Group - similar reacting properties.
SIMILAR not identical
Period - ever increasing proton number
Answer 2: elements in the same period have the same amount of energy levels (in which electrons orbit around the atomic nucleus)elements in the same group have the same number of valance electrons (which are found in the outer most energy level)

ANSWERED AT 06/12/2019 - 01:25 PM

QUESTION POSTED AT 06/12/2019 - 01:25 PM

How wide is the moon

The moon is very nearly a sphere (ball shape).  We usually talk
about the "diameter" of a sphere, not its width. 

The moon's diameter is about  2,159 miles or 3,475 kilometers. 
That's about  27% (a little over a quarter) of the Earth's diameter.

ANSWERED AT 06/12/2019 - 01:24 PM

QUESTION POSTED AT 06/12/2019 - 01:24 PM

Suppose you ride your bicycle to the library traveling at 0.5 km/min. It takes you 25 minutes to get to the library. How far did you travel?

If you cover 0.5 km every minute, and keep it up for 25 minutes,
then you will cover

0.5  +  0.5  +  0.5  +  0.5  +  0.5  +
0.5  +  0.5  +  0.5  +  0.5  +  0.5  +
0.5  +  0.5  +  0.5  +  0.5  +  0.5  +
0.5  +  0.5  +  0.5  +  0.5  +  0.5  +
0.5  +  0.5  +  0.5  +  0.5  +  0.5     =   12.5 km.

An easier way to write the same thing is

             (25) times (0.5 km)  =  12.5 km.

ANSWERED AT 06/12/2019 - 12:53 PM

QUESTION POSTED AT 06/12/2019 - 12:53 PM

how many decimeters equal 1 milliliter

"Decimeter" is a unit of length or distance, whereas "milliliter" is
a unit of volume.  They measure different quantities, and have
different physical dimensions.  Neither one can be converted to
the other one.

If it were possible to convert volume to length or distance, you
(or someone with a better handle on his math and physics) could
figure out how many inches of milk you poured on your cereal.

ANSWERED AT 06/12/2019 - 12:51 PM

QUESTION POSTED AT 06/12/2019 - 12:51 PM

What do you think is the difference between being imaginative in doing science and Doing pseudoscience?

I would say that being imaginative in science means finding new ways to find or analyse the data, but which do not make the data false or which do not manipulate the data. Being imaginative in science should not cross the boundary of making the science not reliable

Being imaginative in pseudoscience could mean manipulating the data or even making experiments in such a way as to only obtaining specific data or throwing away certain data. 

ANSWERED AT 06/12/2019 - 12:44 PM

QUESTION POSTED AT 06/12/2019 - 12:44 PM

The gravitational attraction between two objects will ________if one object acquires more mass

The gravitational force between two objects is proportional to the
product of their two masses.  So if either object acquires more mass,
the magnitude of the gravitational attraction between them increases.

Here is a translation of the same statement, into simple English:

If you are on Earth, and your mass increases because you ate a lot,
then your weight will increase.  

ANSWERED AT 06/12/2019 - 12:43 PM

QUESTION POSTED AT 06/12/2019 - 12:43 PM

Can lunar eclipses only be found in the fall?

A solar eclipse or lunar eclipse can occur at any moment of any day of the year.

ANSWERED AT 06/12/2019 - 12:40 PM

QUESTION POSTED AT 06/12/2019 - 12:40 PM

A stars mass determines ?

A star mass determines Core temperture

ANSWERED AT 06/12/2019 - 12:29 PM

QUESTION POSTED AT 06/12/2019 - 12:29 PM

Critical thinking requires that _______.

Conclusions be adjusted as necessary to incorporate new knowledge.
Hope this helps =)
im taking an integrated physics and chemistry test rite now! 

ANSWERED AT 06/12/2019 - 12:28 PM

QUESTION POSTED AT 06/12/2019 - 12:28 PM

Describe how velocity changes with time

Speeding up, slowing down, and changing direction ... like moving along a curve ... are all changes in velocity. They're also all accelerations.

ANSWERED AT 06/12/2019 - 12:23 PM

QUESTION POSTED AT 06/12/2019 - 12:23 PM