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2 years ago

A stationary rock on a hill has

Physics

2 answers:

Mekhanik [1.2K]2 years ago

5 0

Answer: potential energy but no kinetic energy

Explanation:

Since the rock is stationary, velocity is zero, therefore no kinetic energy,but there's potential energy because the rock is at rest,

Tresset [83]2 years ago

3 0

Answer:

C. Potential energy but no kinetic energy

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A heat pump is to be used for heating a house in winter. The house is to be maintained at 70°F at all times. When the temperatur

Anna35 [415]

Answer:

$\dot{W_{H} } = 4244.48 Btu/h$

Explanation:

Temperature of the house, $T_{H} = 70^{0} F$

Convert to rankine, $T_{H} = 70^{0}+ 460 = 530 R$

Heat is extracted at 40°F i.e $T_{L} = 40^{0}F = 40 + 460 = 500 R$

Calculate the coefficient of performance of the heat pump, COP

$COP = \frac{T_{H} }{T_{H} - T_{L} } \\COP = \frac{530 }{530 - 500 }\\ COP = \frac{530}{30} \\COP = 17.67$

The minimum power required to run the heat pump is given by the formula:

$\dot{W_{H} } = \frac{\dot{Q_{H} }}{COP} \\$ ...............(*)

Where the heat losses from the house, $\dot{Q_{H} } = 75,000 Btu/h$

Substituting these values into * above

$\dot{W_{H} } = \frac{75000}{17.67} \\ \dot{W_{H} } = 4244.48 Btu/h$

3 0

2 years ago

An electromagnetic wave of intensity 150 W/m2 is incident normally on a rectangular black card with sides of 25 cm and 30 cm tha

LenKa [72]

Answer:

3.75 × 10⁻⁸ N

Explanation:

Given:

Intensity of the electromagnetic wave, I = 150 W/m²

Sides of the board = 25 cm (= 0.25 m) and 30 cm (= 0.30 m)

therefore,

the area of the rectangular box, A = 0.25 × 0.30 = 0.075 m²

Now,

force exerted on the card by the radiation, F = $\frac{IA}{C}$

here,

C is the speed of the light = 3 × 10⁸ m/s

on substituting the respective values, we get

F = $\frac{150\times0.075}{3\times10^8}$

F = 3.75 × 10⁻⁸ N

5 0

2 years ago

What did copernicus say about the motion of the sun?.

eimsori [14]

the sun was stationary in the center of the universe and the earth revolved around it....

8 0

2 years ago

Which factor indicates the amount of charge on the source charge?

Westkost [7]

Answer:

B. the number of field lines on the source charge

Explanation:

As we know that electric flux is defined as the number of electric field lines passing through a given area.

So here electric flux due to a point charge "q" is given by

so here we know that flux depends on the magnitude of charge and hence we can say that number of filed lines originating from a point charge will depends on the magnitude of the charge.

3 0

3 years ago

From the top of a cliff, a person tosses a pebble straight downward with an initial velocity of -9.0 meters/second. After 0.50 s

Irina-Kira [14]

Y - yo = Vo*t - g * (t^2) / 2

Vo = - 9.0 m/s
t = 0.50 s

=> y - yo = -9.0 m/s * 0.5 s - 9.8 m/s^2 * (0.5s)^2 / 2 = - 4.5m - 1.225m = - 5.725 m.

Answer: option c) - 5.7

8 0

3 years ago