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IgorLugansk [536]

3 years ago

7

Roads often have to be repaved because they crack over time. Sometimes this cracking is due to the fact that the roads (as well

as other objects) have a tendency to expand when heated and contract when cooled. Thermal expansion and contraction are examples of
A.
physical and chemical changes.
B.
physical changes.
C.
chemical changes.
D.
neither physical nor chemical changes.

1 answer:

Finger [1]3 years ago

4 0

B. Physical Change - T<span>he molecules do not change shape or size. They do not contract or expand only.</span>

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You wish to place a spacecraft in a circular orbit around the earth so that its orbital speed will be 4.00×103m/s. What is this

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Answer:

The radius of orbit= $2.49\times 10^7 m$

Explanation:

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Where G= Gravitational constant

M=Mass of earth

r=Radius of orbit

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$4\times 10^3=\sqrt{\frac{6.67\times 10^{-11}\times 5.972\times 10^{24}}{r}$

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4 years ago

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4 years ago

Find the kinetic energy ofan electron that moves at half the speed of light to four significant digits.

Vlad1618 [11]

Answer:

Ke=electron kinetic energy= $10.24*10^{33} J$

Explanation:

The electron has a mass of $9.1*10^{-31} kg$

The speed of light in a vacuum is a universal constant with the value 299 792 458 m / s (186 282,397 miles / s), although it is usually close to $3*10^{8} \frac{m}{s}$

Kinetic energy (K) is the energy associated with bodies that are in motion, depends on the mass and speed of the body and is calculated using the formula:

$K=\frac{1}{2} *m*v^{2}$ Equation(1)

K=kinetic energy (J)

m =mass of the body (kg)

v= speed of the body $(\frac{m}{s} )$

for this problem We replace in the equation (1)

$me=9.1*10^{-31} kg$ = electron mass

$ve=1.5*10^{8} \frac{m}{s}$ =Half the speed of light

=electron speed

We replace in the equation (1) :

$Ke=\frac{1}{2}*me*ve^{2}$

$Ke=\frac{1}{2} *9.1*10^{-31} *(1.5*10^{8} )^{2}$

$Ke=4.55*10^{-31} *(1.5)^{2} *(10^{8} )^{2}$

$Ke=10.24*10^{33} J$

The energy kinetic of the electron is $10.24*10^{33} Joules$

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3 years ago