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4 years ago

Which of the following directly contributed to soil erosion on the Great Plains in the 1930s?

Physics

1 answer:

NISA [10]4 years ago

4 0

Answer:

Farming

Explanation:

There were three droughts in the 1930s.

Farmers had deep plowed the land and killed the native grasses that trapped soil and moisture.

During the droughts, the moisture evaporated, and the loose soil turned to dust.

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An archer shoots an arrow at an 85.0 m distant target; the bulls eye of the target is at same height as the release height of th

inessss [21]

Answer:

a) 14.1°

b) over

Explanation:

The usual model of ballistic motion assumes that the only force on the flying object is that due to gravity. When an object is launched with initial velocity v0 at some angle θ with respect to the horizontal, the distance it travels is ...

d = (v0)²sin(2θ)/g

Using this relation, we can find the launch angle to make the object travel a given distance:

θ = 1/2arcsin(dg/v0²) . . . . where g is the acceleration due to gravity

For the arrow to hit a target 85 m away at the same height it was launched with speed 42.0 m/s, the launch angle must be ...

θ = 1/2arcsin(dg/v0²) = 1/2(arcsin(85·9.8/42²)) ≈ 14.0893°

The arrow must be released at an angle of about 14.1°.

The flight time to the tree at a distance of 42.5 m will be that distance divided by the horizontal speed:

t = 42.5/(42cos(14.0893°)) ≈ 1.0433 . . . . seconds

The height at that time is ...

h(t) = -4.9t² +42sin(14.0893°)t ≈ 5.33 . . . meters

The arrow will go <em>over</em> the branch.

_____

<em>Additional comment</em>

Since gravity provides the only force on the arrow, its horizontal speed is constant at vh = v0·cos(θ), when the arrow is launched with speed v0 at angle θ above the horizontal. Its vertical speed will be reduced by the acceleration of gravity, so will be vv = v0·sin(θ) -gt. The height is the integral of the vertical speed, so is ...

h(t) = (1/2)gt² +v0·sin(θ)t

The height will be 0 at t=0 and at t=2v0sin(θ)/g, so the horizontal distance traveled will be ...

d = vh·t

= (v0·cos(θ))(2v0·sin(θ)/g) = (v0²/g)(2·sin(θ)cos(θ))

= v0²sin(2θ)/g

Note that this is all simplified by the fact that the target and launch point are at the same level (h=0).

6 0

3 years ago

About how long does it take the sun to rotate once about its axis?

Troyanec [42]

Very very roughly, an Earth month.

The Sun isn't solid, so it doesn't all have to rotate at the same rate. Different latitudes actually rotate at different speeds. One complete rotation is about 24 days at the Sun's equator, but 35 days near the poles !

6 0

3 years ago

g Warm water in a geothermal heating system enters the pipe of a radiator at 20 psia and 119oF with a flow rate of 235 cfm (ft3/

Vika [28.1K]

Answer:

See explanation

Explanation:

Notice that the condenser section includes both the hot water and space heater and station (3) is specified as being in the Quality region. Assume that 50°C is a reasonable maximum hot water temperature for home usage, thus at a high pressure of 1.6 MPa, the maximum power available for hot water heating will occur when the refrigerant at station (3) reaches the saturated liquid state. (Quick Quiz: justify this statement). Assume also that the refrigerant at station (4) reaches a subcooled liquid temperature of 20°C while heating the air.

Using the conditions shown on the diagram and assuming that station (3) is at the saturated liquid state

a) On the P-h diagram provided below carefully plot the five processes of the heat pump together with the following constant temperature lines: 50°C (hot water), 13°C (ground loop), and -10°C (outside air temperature)

b) Using the R134a property tables determine the enthalpies at all five stations and verify and indicate their values on the P-h diagram.

c) Determine the mass flow rate of the refrigerant R134a. [0.0127 kg/s]

d) Determine the power absorbed by the hot water heater [2.0 kW] and that absorbed by the space heater [0.72 kW].

e) Determine the time taken for 100 liters of water at an initial temperature of 20°C to reach the required hot water temperature of 50°C [105 minutes].

f) Determine the Coefficient of Performance of the hot water heater [COPHW = 4.0] (defined as the heat absorbed by the hot water divided by the work done on the compressor)

g) Determine the Coefficient of Performance of the heat pump [COPHP = 5.4] (defined as the total heat rejected by the refrigerant in the hot water and space heaters divided by the work done on the compressor)

h) What changes would be required of the system parameters if no geothermal water loop was used, and the evaporator was required to absorb its heat from the outside air at -10°C. Discuss the advantages of the geothermal heat pump system over other means of space and water heating

4 0

3 years ago

Approximately how much electrical energy does a 5-W lightbulb convert to radiant and thermal energy in one hour?

k0ka [10]

Answer:

18,000 j

Explanation:

the lightbulb dissipates 5W of power

P = ΔE / Δt

rearrange to solve for energy

ΔE = PΔt

P = 5W

t = 1 hour = 60 minutes = 3600 seconds

ΔE = 5 * 3600

ΔE = 18000 J

8 0

3 years ago

At a given instant in time, two cars are traveling at different velocities, one twice as large as the other. Based on this infor

Sati [7]

Answer: No, is not possible.

Explanation:

We have two cars traveling at different velocities, one with velocity v and other with velocity 2*v

We want to know of it is possible to say which of these two cars has the larger acceleration at this instant of time.

Acceleration is the rate of change of the velocity, for example, if acceleration = 0, the velocity does not change.

Notice that knowing only the velocity at a given instant of time, we do not have any way of knowing the acceleration of each car.

Such that acceleration is given by the second Newton's equation:

F = m*a

force equals mass times acceleration.

We do not know any of these quantities for the cars, so we can not say anything about the accelerations.

We also could know the average acceleration if we know the change in velocity over an interval of time, such that:

Av acceleration = (change in velocity)/(interval of time)

But here we do not have a change in velocity, so again, we can't say anything about the acceleration.

3 0

3 years ago