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3 years ago

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In winter the air just above the top bunk of a bunk bed is warmer than the air just above the bottom bunk because warm air rises

. Which of the following describes the method of heating that causes this difference in temperature?

1 answer:

kaheart [24]3 years ago

8 0

Answer:

the heating method in here is conventional heating due to the warn air goes to the top bunk whereas the cold air sinks down

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A woman (mass= 50.5 kg) jumps off of the ground, and comes back down to the ground at a velocity of -8.4 m/s.

Blizzard [7]

Answer:

Approximately $1.6\times 10^{3}\; \rm N$ .

Explanation:

By the Impulse-Momentum Theorem, the change in this woman's momentum will be equal to the impulse that is applied to her.

The momentum $p$ of an object is equal to the product of its mass $m$ and velocity $v$ . That is: $p = m \cdot v$ .

Let $v(\text{before})$ and $v(\text{after})$ represent the velocity of the woman before and after the landing. Let $m$ represent the woman's mass.

The woman's momentum before the landing would be $m \cdot v(\text{before})$ .
The woman's momentum after the landing would be $m \cdot v(\text{after})$ .

Therefore, the change in this woman's momentum would be:

$\begin{aligned}& \Delta p \\ & = p(\text{after}) - p(\text{before}) \\ &= m \cdot (v(\text{after})- v(\text{before}))\end{aligned}$ .

On the other hand, impulse is equal to force multiplied by the duration of the force. Let $F$ represent the average force on the woman. The impulse on her during the landing would be $F \cdot t$ .

Apply the Impulse-Momentum Theorem.

Impulse: $F\cdot t$ .
Change in momentum: $m \cdot (v(\text{after})- v(\text{before}))$ .

Impulse is equal to the change in momentum:

$F \cdot t = m \cdot (v(\text{after})- v(\text{before}))$ .

After landing, the woman comes to a stop. Her velocity would become zero. Therefore, $v(\text{after}) = 0\; \rm m \cdot s^{-1}$ .

$\begin{aligned}F &= \displaystyle \frac{m \cdot (v(\text{after})- v(\text{before}))}{t} \\ &= \frac{50.5\; \text{kg} \times \left(0 \; \mathrm{m \cdot s^{-1}}- 8.4\; \mathrm{m \cdot s^{-1}}\right)}{0.27\; \rm s} \\ &\approx 1.6 \times 10^{3}\; \rm N\end{aligned}$ .

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4 years ago

A rotating turbine generates electricity to power a blow dryer what is the energy transformation

liraira [26]

Electric energy is transformed into mechanical energy of the dryer's engine and heat of the dryer's heater unit.

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4 years ago

A long, thin solenoid has 390 turns per meter and a radius of 1.20 cm. The current in the solenoid is increasing at a uniform ra

gtnhenbr [62]

To solve this problem it is necessary to apply the concepts related to Faraday's law and the induced emf.

By definition the induced electromotive force is defined as

$\int E dl = -\frac{d\phi}{dt}$

$\int E dl = -(\frac{dB}{dt})A$

Where,

$\phi =$ Electric field

B = Magnetic Field

A = Area

At the theory the magnetic field is defined as,

$B = \mu_0 NI$

Where,

N = Number of loops

I = current

$\mu_0 =$ Permeability constant

We know also that the cross sectional area, is the area from a circle, and the length is equal to the perimeter then

A = \pi r^2

l = 2\pi r

Replacing at the previous equation we have that

$E (2\pi r) = \mu_0 n (\frac{di}{dt})(\pi R^2)$

Where,

R = Radius of the solenoid

r = The distance from the axis

Re-arrange to find the current in function of time,

$\frac{di}{dt} = \frac{Er}{\mu_0 NR^2}$

Replacing our values we have

$\frac{di}{dt} = \frac{(8.00*10^{-6})(0.0348)}{(4\pi*10^{-7})(390)(1.2*10^-2)^2}$

$\frac{di}{dt} = 3.94487A/s$

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