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3 years ago

Who was the first known contributor to the atomic theory? Select one: a. Thomson b. Bohr c. Dalton d. Democritus

1 answer:

6 0

It would be D Democritus
He contributed in around 460-370 BC
Whereas the others contributed much later from around 1700's - 1900's

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For work to be done on an object,

djverab [1.8K]

Answer:B

Explanation:

For work to be done, the object must move some distance as a result of a force

3 0

3 years ago

You are traveling at 14 m/s for 20 seconds. What is your displacement?

enyata [817]

Velocity = 14 m/s

Time = 20 s

Displacement = Velocity×Time = (14×20) m = 280 m

The displacement is 280 m towards the direction of motion.

5 0

3 years ago

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A 250 kg car has 6875 kg•m/s of momentum. What is it’s velocity?

liraira [26]

Answer:

v = 27.5 m/s

Explanation:

p = m × v

6,875 = 250 × v

250v = 6,875

v = 6,875/250

v = 27.5 m/s

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3 years ago

A helicopter lifts a 72 kg astronaut 15 m vertically from the ocean by means of a cable. The acceleration of the astronaut is g/

NemiM [27]

Answer:

a) $F_H=776.952\ N$

b) $F_g=706.32\ N$

c) $v=5.4249\ m.s^{-1}$

d) $KE=1059.48\ J$

Explanation:

Given:

mass of the astronaut, $m=72\ kg$

vertical displacement of the astronaut, $h=15\ m$

acceleration of the astronaut while the lift, $a=\frac{g}{10} =0.981\ m.s^{-2}$

<u>Now the force of lift by the helicopter:</u>

Here the lift force is the resultant of the force of gravity being overcome by the force of helicopter.

$F_H-F_g=m.a$

where:

$F_H=$ force by the helicopter

$F_g=$ force of gravity

$F_H=72\times 0.981+72\times9.81$

$F_H=776.952\ N$

The gravitational force on the astronaut:

$F_g=m.g$

$F_g=72\times 9.81$

$F_g=706.32\ N$

Since the astronaut has been picked from an ocean we assume her initial velocity to be zero, $u=0\ m.s^{-1}$

using equation of motion:

$v^2=u^2+2a.h$

$v^2=0^2+2\times 0.981\times 15$

$v=5.4249\ m.s^{-1}$

Hence the kinetic energy:

$KE=\frac{1}{2} m.v^2$

$KE=0.5\times 72\times 5.4249^2$

$KE=1059.48\ J$

8 0

3 years ago

Read 2 more answers

Hiaaa I need help pwease" concerning the planetary orbits why was Copernicus somewhat inaccurate?"

Yuki888 [10]

Copernicus's heliocentric theory stated that the planets orbited in perfectly circular orbits. In reality, they are shaped like ellipses (ovals).

4 0

3 years ago