Basic Science - Class 9 General Knowledge - Extra Questions

1. Reflection
2. Translation
3. Resizing
   

Mechanical energy is not always conserved.

Explanation:

Mechanical energy is the sum of kinetic and potential energy in a system.

$$E_{mech} = K+U$$

Mechanical energy is conserved so long as we ignore air resistance, friction, etc. When we don't ignore outside forces, such as those just mentioned, mechanical energy is not conserved.

Energy is "lost" to friction in the sense that it is not converted between potential and kinetic energy but rather into heat energy, which we cannot put back into the object. If we expand our system to include the entire universe, total energy is conserved, but mechanical energy is not. When the object comes to rest and all of its energy has been lost to friction, $$E_{mech} = 0$$

$$E_{system} =E_{mech} + E_{thermal} = K+U+E_{th}$$

Average distance to Sun is 92.96 MILLION MILES.

Explanation:

diving by 70=1384571 hours.

Average distance to Sun is 92.96 MILLION MILES.

Explanation:

diving by 70=1384571 hours.

By Newton's second law

$$F=ma$$

Plug in the numbers:

$$F = (66kg)(2ms^{-2})$$

$$F = 132N$$

Loss in potential energy = Gain in  kinetic energy.

$$\frac{1}{2} k x^{2}=\dfrac{1}{2} m v^{2}$$

$$\Rightarrow 360 \times(0.06)^{2}=0.2 \times v^{2}$$

$$\Rightarrow v^{2}=\dfrac{360 \times(0.06)^{2}}{0.2}$$

$$\Rightarrow v=2.54 \mathrm{m} / \mathrm{s}$$

When you burn 6.25 moles of methane, you produce 6.25 moles of carbondioxide.

Your reaction is wrong though. I want to correct it.

$$ CH_4 + 2O_2 \rightarrow CO_2+ 2H_2 O $$

hen you burn 6.25 moles of methane, you need 12.5 moles of oxygen gas.

When you burn 6.25 moles of methane, you produce 6.25 moles of carbondioxide $$ ( 27 grams CO_2 ) $$ and  12.5 moles of water vapour (225 grams of $$ H_2O ) $$

$$\% \mathrm{Mg}=\frac{24.3}{58.3} \times 100=41.7 \%$$

$$\% \mathrm{O}=\frac{2 \times 16}{58.3} \times 100=54.9 \%$$

$$\% \mathrm{H}=\frac{2 \times 1}{58.3} \times 100=3.4 \%$$

The molar mass of $$M g(O H)_{2}$$ is 58.3 gmol $$^{-1}$$. The formula mass contains one mole of $$M g\left(24.3 \mathrm{gmol}^{-1}\right)$$ and two moles each of $$O\left(16 \mathrm{gmol}^{-1}\right)$$ and hydrogen $$H$$ (1 $$\left.g m o l^{-1}\right)$$

The mass of magnesium in $$97.4 \ g $$ of $$ Mg(OH)_2$$ is 41.7 % of 97.4 g :  $$ 41.7 \times \dfrac{97.4}{100} = 40.6 \ g$$

Intermolecular forces are found between molecules.

Molecules have a certain influence on their environment. You can, for example, have two molecules with a negative charge that will repel each other due to the intermolecular Coulomb force.

Consider the delocalization of electron density. That is when electron density is spread as much as possible throughout a molecule so that the minimum charge buildup is present in a given orbital.

That is described:

• collectively by all the resonance contributors in Lewis structures.
• collectively by all the individual molecular orbital contributions in molecular orbital diagrams.

Of course, the electronic charge of the ion depends on the number of positively charged nuclear particles, versus the number of fundamental negatively charged particles: i.e. protons versus electrons. Since there are 2 more positive charges than electrons, the charge is +2.

Now, not only can we determine the charge of the ion, we can determine the identity of the ion. How? Because the number of protons, Z, positively charged nuclear particles, determines the identity of the element. What is it?

We have the identity of the element, the number of neutrons, neutrally charged, massive nuclear species, tells us which isotope.

For example, we could represent the deuterium isotope as $$^2H$$. Because it is an hydrogen atom, Z = 1; there is 1 proton, 1 positively charged nuclear particles. Because this is a neutral atom, I know there is 1 electron. But, there is another massive particle in the nucleus (why?), a neutron, and here deuterium is distinguished from the common variety of $$^1$$H nucleus

Explanation:

The atomic number for any element is the number of protons in its atomic nuclei. In a neutral atom, the number of electrons are the same as the number of protons. The atomic mass  (mass number) is the sum of the protons and neutrons in the nucleus, mass number can vary due to the fact that the number of neutrons can vary. Isotopes are named for their mass numbers.

So, this element has 15 protons (atomic number), 15 electrons, and 16 neutrons (mass number minus atomic number).

This isotope is phosphorus-31, which has atomic number 15.

These isotopes of fluorine have $$9$$ proton, $$9$$ electrons and $$10$$ neutrons.

Explanation:

The atomic number is the number of protons (p+). In a neutral atom, the number of electrons (e−) equals the number of protons. The mass number is the sum of the protons and neutrons of a particular isotope. Subtract the atomic number from the mass number to get the number of neutrons. 

Mass number$$−$$atomic number $$=$$ number of neutrons.

There are:
9 protons
9 electrons
10 neutrons

Fluorine is the element in question, as its atomic number is 9. 

The nuclear or isotopic notation would be $$_9^{19}F$$.

Such atoms are called isotopes of each other.

Explanation:

Atoms which have the same number of protons but different numbers of neutrons in the nucleus are known as isotopes.

Because of the difference in the number of neutrons, they will have the same atomic number, but varying atomic mass(or mass number).

the strong force, electromagnetism, weak force, gravity.

Explanation:

"•The strong interaction is very strong but very short-ranged. It acts only over ranges of order $$10^{-13}$$ centimeters and is responsible for holding the nuclei of atoms together. It is basically attractive, but can be effectively repulsive in some circumstances.

• The electromagnetic force causes electric and magnetic effects such as the repulsion between like electrical charges or the interaction of bar magnets. It is long-ranged but much weaker than the strong force. It can be attractive or repulsive and acts only between pieces of matter carrying an electrical charge.

• The weak force is responsible for radioactive decay and neutrino interactions. It has a very short range and, as its name indicates, it is very weak.

• The gravitational force is weak but very long-ranged. Furthermore, it is always attractive and acts between any two pieces of matter in the Universe since mass is its source. "

The derivative of a function at any given point is simply the instantaneous rate of change of the function at that point. In the case of a graph of position (or distance) vs. time, that means that the derivative at a given point $$p_0 (t_0, x_0)$$ is the instantaneous rate of change in position (accounting for "positive" and "negative" direction) with respect to time.

As an example, consider a linear distance function (that is, one which can be represented with a line as opposed to a curve). If this were a function of x and y, with y as the dependent variable, then our function in slope-intercept form would take the form $$y = mx + b,$$ where m is the slope and b is the value of y at $$x = 0.$$ In this case, 

t increases, x increases by 2 units. If we were to, for example, assign units of seconds to t and feet to x, then every second that passed (that is, every increase of one second in t), position (or distance) would increase by two feet (that is x would increase by two feet)

Since our change in distance per unit of change in time will remain the same no matter our starting point $$(x_0, t_0)$$ in this case we can be assured that our instantaneous velocity is the same throughout. Specifically, it is equal to $$m = 2.$$ Differentiating the function with respect to 

• The de Broglie equation is an equation used to describe the wave properties of matter or particles. de Broglie suggested that particles can exhibit properties of waves, and proved that every moving particle has a matter wave associated with it.

The wavelength of the wave depends on the mass and the velocity of the particle:

$$ \lambda = \dfrac{h}{mv} $$ 

• $$ \lambda $$ is wavelength in $$m$$.
• $$h = 6.626 \times 10^{-34}\ J \cdot s $$ is Planck's constant.
• $$m$$ is the mass of a particle in kg moving at a velocity v in m/s. 

D = total distance traveled to reach the office=10 km

consider the motion  during walk

v = speed of surekha during walk =8 km/h

d = distance traveled during walk =0.5 km

t = time spent during walk

Time spent during walk can be given as

t=d/v

t=0.5/8

t=0.0625h

consider the motion during travel by bus :

V = speed of bus =40 km/h

d' = distance remaining to travel to reach office =D−d=10−0.5=9.5 km

t' = time spent in traveling by bus

time spent in traveling by bus is given as

t′=d′/V

t′=9.5/40

t′=0.2375h

Total time taken to reach the office is given as

T=t+t′

T=0.0625+0.2375

T=0.3h

T=0.3×60minutes=18minutes

FORCE
It is the push or pull on an object
THRUST
It is the reaction force acting on an accelerated object because of applied force.

Explanation:

FORCE
It is the push or pull on an object which may change or may not change the state of the object depending upon its amount.
If unopposed, force accelerates the object in its direction.

Force may increase or decrease the velocity of the object.

THRUST

It is the reaction force acting on an accelerated object because of applied force.
Thrust acts on the accelerated object in the direction opposite to the applied force hence it accelerates the object in the direction opposite to the applied force.