Our solar system was created by the gravitational collapse of the

A garrafa térmica (também conhecida como "vaso de Dewar") é um dispositivo extremamente útil para conservar, no seu interior, co

igor_vitrenko [27]

Answer:

A opção A está correta.

O sistema formado pela garrafa térmica e a água perde 400 cal de calor para o meio ambiente.

Option A is correct.

The system formed by the thermos and the water loses 400 cal of heat to the environment.

Explanation:

Quando a temperatura de um sistema reduz, fica claro que o sistema perdeu calor ou energia térmica. Como a temperatura é um dos indicadores mais claros disso, esta conclusão é hermética e correta.

Mas, para saber a quantidade de calor perdida para o meio ambiente, agora fazemos alguns cálculos de energia térmica.

Transferência de calor de ou para o sistema de água e garrafa térmica = c × ΔT

c = capacidade térmica do sistema de água e garrafa térmica = 80 cal /°C

ΔT = Alteração da temperatura do sistema de água e garrafa térmica = (temperatura final) - (temperatura inicial) = 55 - 60 = -5°C

Calor transferido = 80 × -5 = -400 cal.

O sinal de menos mostra que o calor é transferido para fora do sistema, ou seja, o calor é perdido no sistema.

Espero que isto ajude!!!

English Translation

The thermos (also known as "Dewar vase") is an extremely useful device to conserve bodies (essentially liquid) at high temperatures, minimizing energy exchanges with the environment, which is generally colder. A thermos contains water at 60 o C. The thermos + water set has a thermal capacity of C = 80 cal / o C. The system is placed on a table and, after a considerable period of time, its temperature decreases to 55 o C. In this case, it is concluded that the system formed by the thermos and the water inside:

a) lost 400 cal. B) gained 404cal. C) lost 4 850 cal. D) gained 4 850 cal. E) did not exchange heat with the external environment.

Solution

When a system's temperature reduces, it is clear to conclude that the system has lost heat or thermal energy. Since temperature is one of clearest indicators of this, this conclusion is airtight and correct.

But, to know the amount of heat lost to the environment, we now do some thermal energy calculations.

Heat transferrred from or to the water and thermos system = c × ΔT

c = heat capacity of the water and thermos system = 80 cal/°C

ΔT = Change in temperature of the water and thermos system = (final temperature) - (initial temperature)

= 55 - 60 = -5°C

Heat transferred = 80 × -5 = -400 cal.

The minus sign shows that the heat is transferred out of the system, that is, the heat is lost from the system.

Hope this Helps!!!

7 0

3 years ago

A projectile is fired with a velocity of 400 ms-1 at an angle of 30° to the horizontal. Find the time to reach the greatest heig

nexus9112 [7]

Answer:

Greatest height = 2040m (to 3 significant figures)

Horizontal displacement to the point of greatest height = 7060m (to 3 significant figures)

Explanation:

First, we want to find the greatest height reached;

In other words, we are asked to find the maximum vertical displacement;

What should be known is that vertical quantities are, for all intents and purposes really, independent and thus unaffected by horizontal factors at play;

We can therefore calculate and proceed considering the two perpendicular planes separately;

So, we now need to consider what we know, what we need to find and what we can deduce:

We know, as given, the initial velocity and we need to find the displacement, this should indicate that we need to use the SUVAT or kinematic equations/formulas;

We can deduce that the vertical velocity at the maximum height will be 0 because at the greatest height, the projectile will no longer ascend, it will stop and then begin to fall;

And since there is a change in velocity, there is acceleration involved as well;

We are not told of any capacity of the projectile itself to accelerate so we can assume there is no acceleration from it and this leaves only gravity to consider in the vertical dimension as acceleration:

So, to summarise nicely all of the information:

u = initial velocity (m/s) = 400

$s_{v}$ = vertical displacement or the height reached (m)

$v_{v}$ = final vertical velocity (m/s) = 0

$a_{v}$ = vertical acceleration (m/s²) = -9.81 (i.e. gravity)

The relevant SUVAT or kinematic equation, which involves all of these quantities:

v² = u² + 2as

The only other thing we need to do before we can use this equation to get $s_{v}$ is to get the initial vertical velocity (i.e. $u_{v}$ );

We have the initial velocity and what we can do is split the velocity into it's vertical and horizontal component;

P.S. this is a key concept in any kind of mechanics and physics questions and can be done forces, velocities or even acceleration (really cool XD)

The projection can be illustrated as a right-angle triangle with an angle of 30° and a hypotenuse of 400;

If we want to find the vertical velocity, which is what we want, we need to use trigonometry:

sin(Θ) = opposite/hypotenuse

Substitute in our values and rearrange:

sin (30) = $u_{v}$ /400

$u_{v}$ = 400.sin(30)

$u_{v}$ = 200

Now we can plug all these values in the aforementioned SUVAT equation:

(0)² = (200)² + 2(-9.81)( $s_{v}$ )

0 = 40000 - 19.62( $s_{v}$ )

19.62( $s_{v}$ ) = 40000

$s_{v}$ = ⁴⁰⁰⁰⁰/₁₉.₆₂

$s_{v}$ = 2038.7359836901121304791029561672 → 2040 m

Now, to find how far the horizontal distance is to this point of the greatest height, we need to do something similar except we need to consider the horizontal dimension, not the vertical;

So, once again, we have initial velocity (and we can find the initial horizontal velocity) and we want to find the horizontal displacement;

In terms of acceleration, gravity is negligible since it is a vertical acceleration so it has no effect on the horizontal speed, and by extension no effect on the horizontal displacement;

Air resistance is typically ignored until higher levels of education so we can simply ignore it as well;

This means horizontal acceleration is 0;

So, to summarise:

u = initial velocity (m/s) = 400

$s_{h}$ = horizontal displacement (m)

$a_{h}$ = horizontal acceleration (m/s²) = 0

Since acceleration is 0, there is no change to velocity so there is no initial and final velocity;

This means the relevant equation or formula is (very easy):

v = s/t or commonly known as speed = distance/time

We want to find the distance and we have speed, we just need time;

We can find time because this variable will be the same for initial and horizontal velocities, i.e. the time taken for the projectile to reach the maximum height will be the same as the time taken to reach the point of horizontal displacement we want to find;

So to find the time taken for the vertical displacement, we can use the SUVAT formula:

s = ¹/₂(u + v).t

Plug in the values:

2038.735.... = ¹/₂(200 + 0).t

2038.735.... = 100t

t = 20.38735...

Horizontal velocity will be:

cos(Θ) = adjacent/hypotenuse

cos(30) = $u_{h}$ /400

$u_{h}$ = 400.cos(30)

$u_{h}$ = 346.41016...

Now, we have horizontal velocity and time, we can find the horizontal displacement:

346.41... = $s_{h}$ /20.387...

$s_{h}$ = 346.41...(20.387...)

$s_{h}$ = 7062.38886.... → 7060 m

Its a bit long but is not complicated once you get it

Hope this helps ;D

8 0

3 years ago

Manuel releases a pendulum bob. The drawing shows its path. At which point does the pendulum bob have the most gravitational pot

kati45 [8]

We have no clue until we see the drawing. After all, the drawing shows its path.

7 0

3 years ago

You are throwing a ball straight up in the air. At the highest point, the ball’s

Afina-wow [57]

The answer is C. Acceleration is nonzero, but it’s velocity is zero

8 0

4 years ago

A) The motor speed is less than wheel speed.

n200080 [17]

For the following statements

A) The motor speed is less than wheel speed.

B) The output power of the motor is positive during hill climbing.

C) The wheel torque is more than motor torque

These assertions are given respectively as

false
true
false

<h3>What are speed, power, and Torque?</h3>

Speed: defined as the ratio of operation with respect to distance and time

Power: defined as the ability to work

Torque: This is the speed of a rotating object

Generally, the equation for Speed, Power, Torque is mathematically given as

V=m/s

P=w/t

T=rfsin\theta

In conclusion

For a moving car, the wheels speed is in equilibrium with the motor speed Hence false

The output power during a hill climb is positive cause work is been done, Hence true

The wheel torque also is in equilibrium with the motor Torque, Hence false