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3 years ago

When did jj thomson contribute to the atomic theory?

1 answer:

7 0

In 1897<span>, J.J. Thomson discovered the electron by experimenting with a Crookes, or cathode ray, tube. He demonstrated that cathode rays were negatively charged. In addition, he also studied positively charged particles in neon gas.</span>

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Why cable color codes are important ? what if we use three phase cables without color

Degger [83]

Answer:

Cable color codes are very important for example, If something is not wired properly, it can result in injuries, deaths, fires, and many other problems. This is why there are well-established wire color codes to ensure those working with an around this type of equipment can ensure everything is wired safely and effectively. If we used three phase cables without color code, this can lead too incorrect things that might be a hazard too get not fix and learning new color codes would be hard therefore we should stick too the same color codes for cables and it saves the hassle for needing too check every cable cord color then the original one signed too it.

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3 years ago

Which statements are true concerning Newton's law of gravitation? The gravitational force is related to the mass of each object.

OLEGan [10]

Answer:

The gravitational force is related to the mass of each object.

The gravitational force is an attractive force.

Explanation:

Gravitational force is a long range force of attraction between any two masses.

Mathematically given as :

$F=G.\frac{m_1.m_2}{r^2}$

where:

$m_1 & m_2$ are the masses

r= distance between the center of mass of the two objects.

G= gravitational constant = $6.67\times 10^{-11} m^3.kg^{-1}.s^{-2}$

From the above relation of eq. (1) it is clear that,

Gravitational force is inversely proportional to the square of the distance and directly proportional to the masses.

The mass of an object is independent of its size due to the fact that density may vary for different objects.

The force of gravity varies with height as:

$\frac{g}{g_x} =(\frac{r_x}{r} )^2$

where:

$g=9.8\,m.s^{-2}$

$g_x=$ gravity at height $r_x$ of the center of mass of the object from the center of mass of the earth.

and we know that force:

$F=m\times g$

where: m= mass of the object.

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3 years ago

To meet a U.S. Postal Service requirement, employees' footwear must have a coefficient of static friction of 0.5 or more on a sp

motikmotik

Answer:

0.79 s

Explanation:

We have to calculate the employee acceleration, in order to know the minimum time. According to Newton's second law:

$\sum F_x:f_{max}=ma_x\\\sum F_y:N-mg=0$

The frictional force is maximum since the employee has to apply a maximum force to spend the minimum time. In y axis the employee's acceleration is zero, so the net force is zero. Recall that $f_{max}=\mu N$

Now, we find the acceleration:

$\mu N=ma_x\\\mu mg=ma_x\\a_x=\mu g\\a_x=0.83(9.8\frac{m}{s^2})\\a_x=8.134\frac{m}{s^2}$

Finally, using an uniformly accelerated motion formula, we can calculate the minimum time. The employee starts at rest, thus his initial speed is zero:

$x=v_0t+\frac{1}{2}a_xt^2\\2x=a_xt^2\\t=\sqrt{\frac{2x}{a}}\\t=\sqrt{\frac{2(3.2m)}{8.134\frac{m}{s^2}}}\\t=0.79 s$

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3 years ago

What is the difference between weight and mass? Give an example of how they are different.

marusya05 [52]

Mass is the amount of matter it has, while weight <span>is a measurement of the force placed on an object by gravity. An example of how they are different is that mass is always constant while weight varies depending on the location.</span>

8 0

3 years ago

A sled with no initial velocity accelerates at a rate of 3.2 m/s2 down a hill. How long does it take the sled to go 15 m to the

grin007 [14]

S = ut + 1/2 at^2
a = 3.2 m/s^2
s = 15m
Find t
15 = 1/2(3.2)t^2
15 = 3.2t^2/2
30 = 3.2t^2
30/ 3.2 = 9.38
Square root of 9.38 = 3.06
It takes 3.06 seconds

3 0

3 years ago