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2 years ago

A well-trained athlete can run 400m in 47s, what is the athlete’s velocity?

Physics

1 answer:

AnnZ [28]2 years ago

7 0

Answer:

8.51 m/s

Explanation:

Velocity = Displacement/Time

Velocity = 400 m ÷ 47 s

Velocity = 8.51 m/s

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When the starter motor on a car is engaged, there is a 290 A current in the wires between the battery and the motor. Suppose the

Tema [17]

Answer:

$33.6\times10^{-4}}\text{ m}$ = 3.36 mm

Explanation:

From Ohm's law,

$V = IR$ (Voltage = Current * Resistance)

$R = \dfrac{V}{I}$

The geometric definition of resistance is

$R = \rho\dfrac{l}{A}$

where $\rho$ is the resistivity of the material, $l$ and $A$ are the length and cross-sectional area, respectively.

$A = \rho\dfrac{l}{R}$

$A = \rho\dfrac{l\timesI}{V}$

Since the wire is assumed to have a circular cross-section, its area is given by

$A = \pi\dfrac{d^2}{4}$ where $d$ is the diameter.

$\pi\dfrac{d^2}{4} = \rho\dfrac{l\timesI}{V}$

$d = \sqrt{\dfrac{4\rho l I}{\pi\times V}}$

Resistivity of copper = $1.68\times10^{-8}$ . With these and other given values,

$d = \sqrt{\dfrac{4\times1.68\times10^{-8}\times1.5\times290}{3.14\times 0.55}}$

$d = \sqrt{1128.43\times10^{-8}}$

$d = 33.6\times10^{-4} \text{ m}$

5 0

3 years ago

An ocean thermal energy conversion system is being proposed for electric power generation. Such a system is based on the standar

defon

Answer:

Explanation:

Dear Student, this question is incomplete, and to attempt this question, we have attached the complete copy of the question in the image below. Please, Kindly refer to it when going through the solution to the question.

To objective is to find the:

(i) required heat exchanger area.

(ii) flow rate to be maintained in the evaporator.

Given that:

water temperature = 300 K

At a reasonable depth, the water is cold and its temperature = 280 K

The power output W = 2 MW

Efficiency $\zeta$ = 3%

where;

$\zeta = \dfrac{W_{out}}{Q_{supplied }}$

$Q_{supplied } = \dfrac{2}{0.03} \ MW$

$Q_{supplied } = 66.66 \ MW$

However, from the evaporator, the heat transfer Q can be determined by using the formula:

Q = UA(L MTD)

where;

$LMTD = \dfrac{\Delta T_1 - \Delta T_2}{In (\dfrac{\Delta T_1}{\Delta T_2} )}$

Also;

$\Delta T_1 = T_{h_{in}}- T_{c_{out}} \\ \\ \Delta T_1 = 300 -290 \\ \\ \Delta T_1 = 10 \ K$

$\Delta T_2 = T_{h_{in}}- T_{c_{out}} \\ \\ \Delta T_2 = 292 -290 \\ \\ \Delta T_2 = 2\ K$

$LMTD = \dfrac{10 -2}{In (\dfrac{10}{2} )}$

$LMTD = \dfrac{8}{In (5)}$

LMTD = 4.97

Thus, the required heat exchanger area A is calculated by using the formula:

$Q_H = UA (LMTD)$

where;

U = overall heat coefficient given as 1200 W/m².K

$66.667 \times 10^6 = 1200 \times A \times 4.97 \\ \\ A= \dfrac{66.667 \times 10^6}{1200 \times 4.97} \\ \\ \mathbf{A = 11178.236 \ m^2}$

The mass flow rate:

$Q_{H} = mC_p(T_{in} -T_{out} ) \\ \\ 66.667 \times 10^6= m \times 4.18 (300 -292) \\ \\ m = \dfrac{ 66.667 \times 10^6}{4.18 \times 8} \\ \\ \mathbf{m = 1993630.383 \ kg/s}$

3 0

3 years ago

Convert 43 km/h to m/s.

SIZIF [17.4K]

Answer:

43km/h to m/s = 11.9444

Explanation:

1 km = 1000 m; 1 hr = 3600 sec. To convert km/hr into m/sec, multiply the number by 5 and then divide it by 18.

6 0

3 years ago

I need help real quick. Please help me!!

dimaraw [331]

<h3>Answer;</h3>

D) Standing wave

<h3>Explanation;</h3>

Standing wave also called stationary wave is a wave which oscillates in time but whose peak amplitude profile does not move in space.
A standing wave pattern is a vibrational pattern created within a medium when the vibrational frequency of the source causes reflected waves from one end of the medium to interfere with incident waves from the source.
Examples of standing waves include the vibration of a violin string and electron orbitals in an atom.

4 0

3 years ago

The magnetic field at the equator points north. If you throw a positively charged object (for example, a baseball with some elec

PilotLPTM [1.2K]

Answer:

The magnetic force points in the positive z-direction, which corresponds to the upward direction.

Option 2 is correct, the force points in the upwards direction.

Explanation:

The magnetic force on any charge is given as the cross product of qv and B

F = qv × B

where q = charge on the ball thrown = +q (Since it is positively charged)

v = velocity of the charged ball = (+vî) (velocity is in the eastern direction)

B = Magnetic field = (+Bj) (Magnetic field is in the northern direction; pointing forward)

F = qv × B = (+qvî) × (Bj)

F =

| î j k |

| qv 0 0|

| 0 B 0

F = i(0 - 0) - j(0 - 0) + k(qvB - 0)

F = (qvB)k N

The force is in the z-direction.

We could also use the right hand rule; if we point the index finger east (direction of the velocity), the middle finger northwards (direction of the magnetic field), the thumb points in the upward direction (direction of the magnetic force). Hence, the magnetic force is acting upwards, in the positive z-direction too.

Hope this Helps!!!

5 0

3 years ago