# Dave rows a boat across a river at 4.0 m/s. the river flows at 6.0 m/s and is 360 m across.a. in what direction, relative to the shore, does dave’s boat go? b. how long does it take dave to cross the river? c. how far downstream is dave’s landing point? d. how long would it take dave to cross the river if there were no current?

a) Let's call x the direction parallel to the river and y the direction perpendicular to the river.

Dave's velocity of 4.0 m/s corresponds to the velocity along y (across the river), while 6.0 m/s corresponds to the velocity of the boat along x. Therefore, the drection of Dave's boat is given by:

relative to the direction of the river.

b) The distance Dave has to travel it S=360 m, along the y direction. Since the velocity along y is constant (4.0 m/s), this is a uniform motion, so the time taken to cross the river is given by

c) The boat takes 90 s in total to cross the river. The displacement along the y-direction, during this time, is 360 m. The displacement along the x-direction is

so, Dave's landing point is 540 m downstream.

d) If there were no current, Dave would still take 90 seconds to cross the river, because its velocity on the y-axis (4.0 m/s) does not change, so the problem would be solved exactly as done at point b).

## Related Questions

Explain why it is dangerous to jump from a fast moving train

When you jump off a train, you jump off a certain height and your downwards (vertical) velocity is zero. But your forward (horizontal) velocity is not. You will hit the ground on split second with your horizontal velocity practically the same as the train.

Explanation:

you be in serious injury.

А pressure gauge with a measurement range of 0-10 bar has a quoted inaccuracy of £1.0% f.s. (+1% of full-scale reading). (a) What is the maximum measurement error expected for this instrument? (b) What is the likely measurement error expressed as a percentage of the or reading if this pressure gauge is measuring a pressure of 1 bar?​

Explanation:

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The maximum expected measurement error for a pressure gauge measuring 0-10 bar with an inaccuracy of 1% of full-scale reading is 0.1 bar. When the gauge measures 1 bar, the expected inaccuracy is 10%.

### Explanation:

The inaccuracy mentioned here is related to the full-scale reading which means the error is calculated based on the top measurement value. The pressure gauge range is 0-10 bar, so the inaccuracy is one percent of this. (a) Thus, the maximum measurement error expected for this instrument is 1.0% of 10 bar i.e., 0.1 bar. (b) If the gauge is measuring a pressure of 1 bar, then the relative error expressed as a percentage would be the absolute error (0.1 bar) divided by the observed reading (1 bar) i.e., 10%. It means, when measuring 1 bar pressure, the expected measurement error is 10%. This is an example of how instrument inaccuracy is properly interpreted and employed when working with various measurements.

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Which is the best description of the scientific theory

Explanation:

a scientific theory is a well substantiated explanation of some aspect of the nature world, based on a body of facts that have been repeatedly confirmed through observation and experiment. search fact-supported theories are not "guesses" but reliable account of the real world .

Do you think a baseball curves better at the top of a high mountain or down on a flat plain

The baseball curves better at a flatplain due to contacting with air.

### What is a baseball curve?

A curveball is a breaking pitch with more movement than most other pitches. It is thrown slower and with more overall break than a slider and is used to throw hitters off balance.

On a flat plain, a baseball will curve down better. This is due to the curving being caused by the ball contacting air and being pushed in a specificdirection.

The spin, speed, and location of the ball's stitches in relation to the air will all influence how it changes direction when pushed against.

Consider throwing a baseball in a vacuum where there is no air. Because there is no air to push on the ball, it will not curve at all.

Thus, a flat plain area will be better for baseball curve.

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A baseball will curve better down on a flat plain.In view of the fact that the curving is caused by the ball contacting the air and pushing the ball in a particular direction.

If a coil stays at rest in a very large static magnetic field, no emf is induced in this coil. Group of answer choices True False

True

Explanation:

• Faraday's Law says that there is a emf induced in a conductor when the vector flux of the magnetic field across it changes in time.
• This can be true due to one of two facts, either the magnitude of the magnetic field changes in time, or the area through which the flux occurs changes due to the movement of the object.
• In this case, due to the magnetic field is constant, and the coil stays at rest, there is no possible change in flux, so emf induced is zero.

The interatomic spring stiffness for tungsten is determined from Young's modulus measurements to be 90 N/m. The mass of one mole of tungsten is 0.185 kg. If we model a block of tungsten as a collection of atomic "oscillators" (masses on springs), what is one quantum of energy for one of these atomic oscillators? Note that since each oscillator is attached to two "springs", and each "spring" is half the length of the interatomic bond, the effective interatomic spring stiffness for one of these oscillators is 4 times the calculated value given above. Use these precise values for the constants: ℏ = 1.0546 10-34 J · s (Planck's constant divided by 2π) Avogadro's number = 6.0221 1023 molecules/mole kB = 1.3807 10-23 J/K (the Boltzmann constant)

Explanation:

solution below

The quantum of energy for one atomic oscillator in tungsten, given the effective interatomic spring stiffness of 360 N/m, the mass of one tungsten atom as 3.074 x 10^-25 kg, and the reduced Planck's constant of 1.0546 x 10^-34 J · s, can be calculated to be approximately 1.33 x 10^-21 J.

### Explanation:

To calculate the quantum of energy for one atomic oscillator in tungsten, we will consider the model of an atom being connected to two springs, both having an effective interatomic spring stiffness of four times the given value (90 N/m). This value thus becomes 360 N/m.

One mole of tungsten has a mass of 0.185 kg, thus the mass of one atom can be determined by dividing this value by Avogadro's number (6.0221 x 10^23 molecules/mole), which gives approximately 3.074 x 10^-25 kg.

The quantum of energy, or the energy of one quantum (the smallest possible energy increment), is given by the formula E = ħω, where ħ is the reduced Planck's constant (1.0546 x 10^-34 J · s) and ω is the angular frequency, given by sqrt(k/m), where k is the spring constant and m is the mass.

Substituting the known values into these equations gives ω= sqrt((360)/(3.074 x 10^-25)) and E= (1.0546 x 10^-34) x sqrt((360)/(3.074 x 10^-25)), which results in a quantum of energy of approximately 1.33 x 10^-21 J.