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3 years ago

7

Why do we close our eyes when we sleep

1 answer:

Ksju [112]3 years ago

3 0

Answer:

because our some of the energy goes from our eyes

explanation;

There are several reasons why it's important to close our eyes while we sleep. Closed eyelids block light, which stimulates the brain to wakefulness. Closing our eyes also protects and lubricates the eyes while we sleep

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What must happen to the electrons in a material to create an electric current?

photoshop1234 [79]

Electric current is a stream of electrons in motion, so they have to gain an energy from outside. There are two possibilities: one of them is the photoeletric phenomenom which is based on striking electrons from their orbits with the photon's energy. Second options is the substraction od eletric potentials on the edges od material.

5 0

3 years ago

A stone is dropped from a cliff at time t = 0 and strikes the ground below.

Dafna1 [17]

Answer:

S=

2

1

gt

2

........(1)

And that of the other stone is

S=u(t−n)+

2

1

[g(t−n)

2

]........(2)

Since both the stones meet at the distance so equation (1)and equation(2) will be equal

2

1

gt

2

=u(t−n)+

2

1

[g(t−n)

2

]

gt

2

=2ut−2un+gt

2

+gn

2

−2gnt

t(2gn−2u)=gn

2

−2un

t=

(gn−u)

n(

2

gn

−u)

now putting value of t in equation(1)

s=

2

g

⎣

⎢

⎡

gn−u

2

[n(

2

gn

−u)]

⎦

⎥

⎤

2

S=

2

g

⎣

⎢

⎡

(gn−u)

2

n(

2

gn

−u)

⎦

⎥

⎤

Explanation:

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i will also follow u

5 0

3 years ago

A 12,500 N alien UFO is hovering about the surface of Earth. At time , its position can be given as () = ((0.24 m/s^3)^3 + 25 m)

stepladder [879]

a) $F=(3675i-4543k)N$

b) 5843 N

Explanation:

a)

The position of the UFO at time t is given by the vector:

$r(t)=(0.24t^3+25)i+(4.2t)j+(-0.43t^3+0.8t^2)k$

Therefore it has 3 components:

$r_x=0.24t^3+25\\r_y=4.2t\\r_z=-0.43t^3+0.8t^2$

We start by finding the velocity of the UFO, which is given by the derivative of the position:

$v_x=r'_x=\frac{d}{dt}(0.24t^3+25)=3\cdot 0.24t^2=0.72t^2\\v_y=r'_y=\frac{d}{dt}(4.2t)=4.2\\v_x=r'_z=\frac{d}{dt}(-0.43t^3+0.8t^2)=-1.29t^2+1.6t$

And then, by differentiating again, we find the acceleration:

$a_x=v'_x=\frac{d}{dt}(0.72t^2)=1.44t\\a_y=v'_y=\frac{d}{dt}(4.2)=0\\a_z=v'_z=\frac{d}{dt}(-1.29t^2+1.6t)=-2.58t+1.6$

The weight of the UFO is W = 12,500 N, so its mass is:

$m=\frac{W}{g}=\frac{12500}{9.8}=1276 kg$

Therefore, the components of the force on the UFO are given by Newton's second law:

$F=ma$

So, Substituting t = 2 s, we find:

$F_x=ma_x=(1276)(1.44t)=(1276)(1.44)(2)=3675 N\\F_y=ma_y=0\\F_z=ma_z=(1276)(-2.58t+1.6)=(1276)(-2.58(2)+1.6)=-4543 N$

So the net force on the UFO at t = 2 s is

$F=(3675i-4543k)N$

b)

The magnitude of a 3-dimensional vector is given by

$|v|=\sqrt{v_x^2+v_y^2+v_z^2}$

where

$v_x,v_y,v_z$ are the three components of the vector

In this problem, the three components of the net force are:

$F_x=3675 N\\F_y=0\\F_z=-4543 N$

Therefore, substituting into the equation, we find the magnitude of the net force:

$|F|=\sqrt{3675^2+0^2+(-4543)^2}=5843 N$

7 0

3 years ago

Mechanical energy is the sum total of all the kinetic energy and

dolphi86 [110]

Answer:

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

5 0

3 years ago

HELP<br> as shown in the diagram, points p,q, and r are located near a positively charged object.

tester [92]

I can’t open or look at the image

6 0

3 years ago