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larisa86 [58]
2 years ago
6

Ai là người phát hiện trái đất hình cầu đầu tiên ?

Physics
1 answer:
Scorpion4ik [409]2 years ago
5 0

Answer:

Can't understand the language

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beks73 [17]
Hi there!

Assuming you're asking about the solar system, there are nine planets. But, if you're wanting to know about the universe, there are trillions and trillions of planets (most of which we haven't yet discovered). 

Hope this helps!
5 0
3 years ago
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What is dark energy?
olga2289 [7]

Explanation:

Dark Energy. Dark Energy is a hypothetical form of energy that exerts a negative, repulsive pressure, behaving like the opposite of gravity. It has been hypothesised to account for the observational properties of distant type Ia supernovae, which show the universe going through an accelerated period of expansion

6 0
3 years ago
A quarterback is set up to throw the football to a receiver who is running with a constant velocity v⃗ rv→rv_r_vec directly away
Artist 52 [7]

Answer:

a) V_o,y = 0.5*g*t_c

b) V_o,x = D/t_c - v_r

c) V_o = sqrt ( (D/t_c - v_r)^2 + (0.5*g*t_c)^2)

d)  Q = arctan ( g*t_c^2 / 2*(D - v_r*t_c) )

Explanation:

Given:

- The velocity of quarterback before the throw = v_r

- The initial distance of receiver = r

- The final distance of receiver = D

- The time taken to catch the throw = t_c

- x(0) = y(0) = 0

Find:

a) Find V_o,y, the vertical component of the velocity of the ball when the quarterback releases it.  Express V_o,y in terms of t_c and g.

b) Find V_o,x, the initial horizontal component of velocity of the ball.   Express your answer for V_o,x in terms of D, t_c, and v_r.

c) Find the speed V_o with which the quarterback must throw the ball.  

   Answer in terms of D, t_c, v_r, and g.

d) Assuming that the quarterback throws the ball with speed V_o, find the angle Q above the horizontal at which he should throw it.

Solution:

- The vertical component of velocity V_o,y can be calculated using second kinematics equation of motion:

                               y = y(0) + V_o,y*t_c - 0.5*g*t_c^2

                              0 = 0 + V_o,y*t_c - 0.5*g*t_c^2

                               V_o,y = 0.5*g*t_c

- The horizontal component of velocity V_o,x witch which velocity is thrown can be calculated using second kinematics equation of motion:

- We know that V_i, x = V_o,x + v_r. Hence,

                               x = x(0) + V_i,x*t_c

                               D = 0 + V_i,x*t_c

                               V_o,x + v_r = D/t_c

                                V_o,x = D/t_c - v_r

- The speed with which the ball was thrown can be evaluated by finding the resultant of V_o,x and V_o,y components of velocity as follows:

                           V_o = sqrt ( V_o,x^2 + V_o,y^2)

                          V_o = sqrt ( (D/t_c - v_r)^2 + (0.5*g*t_c)^2)

       

- The angle with which it should be thrown can be evaluated by trigonometric relation:

                            tan(Q) = ( V_o,y / V_o,x )

                            tan(Q) = ( (0.5*g*t_c)/ (D/t_c - v_r) )

                                   Q = arctan ( g*t_c^2 / 2*(D - v_r*t_c) )

                           

                               

6 0
3 years ago
Your heart has four valves. Normally, these valves open to let blood flow through your heart, and then shut to keep it from flow
stiv31 [10]

Answer:

It influences blood flow

7 0
3 years ago
You are doing x-ray diffraction on a crystal that has a cubic structure, using 0.340-nm x rays. Part A If the lattice spacing is
Mrac [35]

Answer:

∅ = 0.26°

Explanation:

Bragg's law states that:

n×λ = 2×d×sin(∅)

<em>where:</em>

  • <em>d is the lattice spacing.</em>
  • <em>λ is the wavelength of the rays.</em>
  • <em>n is the order of the diffracted rays, n = 1.</em>

then:

sin(∅) = λ/2×d

    ∅ = sin^-1(λ/2×d)

    ∅ = 0.26°

6 0
3 years ago
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