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faltersainse [42]

2 years ago

9

Which pair of sentences is describing the same velocity? A car is parked. A car is moving in circles. A bus drives 40 miles per

hour north. A truck drives 50 miles per hour north. A boy walks east at 6 kilometers per hour. A girl walks west at the same speed as the boy. Valerie rides her bike south at 8 kilometers per hour. Owen jogs south at 8 kilometers per hour.

2 answers:

olya-2409 [2.1K]2 years ago

8 0

The bus and the truck have the same velocity.

Also, Valerie and Owen have the same velocity.

Phoenix [80]2 years ago

7 0

Velocity is a vector, so it contains two pieces of information:

- a magnitude, which is given by the speed

- a direction

Two objects, in order to have same velocity, should have both same speed and same direction. In this problem, only the following pair of sentences describe people with same velocity:

Valerie rides her bike south at 8 kilometers per hour.

Owen jogs south at 8 kilometers per hour.

In fact, both Valerie and Owen are moving at same speed (8 km per hour) in the same direction (south), so they have same velocity.

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If the mass of a material is 46 grams and the volume of the material is 14 cm^3, what would the density of the material be?

umka21 [38]

<u>Answer</u>

3.2857 g/cm³

<u>Explanation</u>

Density of a material is the mass of a unit volume of that material. It's SI unit is Kg/m³ but its has other units like g/cm³.

Density = mass/volume

= 46/14

= 3.2857 g/cm³

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3 years ago

The intensity at distance from a spherically symmetric sound source is 100 W/m2. What is the intensity at five times this distan

ss7ja [257]

To solve this problem it is necessary to apply the concepts related to intensity as a function of power and area.

Intensity is defined to be the power per unit area carried by a wave. Power is the rate at which energy is transferred by the wave. In equation form, intensity I is

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The area of a sphere is given by

$A = 4\pi r^2$

So replacing we have to

$I = \frac{P}{4\pi r^2}$

Since the question tells us to find the proportion when

$r_1 = 5r_2 \rightarrow \frac{r_2}{r_1} = \frac{1}{5}$

So considering the two intensities we have to

$I_1 = \frac{P_1}{4\pi r_1^2}$

$I_2 = \frac{P_2}{4\pi r_2^2}$

The ratio between the two intensities would be

$\frac{I_1}{I_2} = \frac{ \frac{P_1}{4\pi r_1^2}}{\frac{P_2}{4\pi r_2^2}}$

The power does not change therefore it remains constant, which allows summarizing the expression to

$\frac{I_1}{I_2}=(\frac{r_2}{r_1})^2$

Re-arrange to find $I_2$

$I_2 = I_1 (\frac{r_1}{r_2})^2$

$I_2 = 100*(\frac{1}{5})^2$

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Many web sites describe how to add wires to your clothing to keep you warm while riding your motorcycle. The wires are added to

Tomtit [17]

Answer:

$P=42.075W$

Explanation:

The power provided by a resistor (wire in this case) is given by:

$P=\frac{V^2}{R}$ .

The resistance of a wire is given by:

$R=\frac{\rho L}{A}$

Where for the resistivity the one of the copper should be used: $\rho=1.68\times10^{-8}\Omega m$ .

The area A is that of a circle, which written in terms of its diameter is:

$A=\pi r^2=\pi (d/2)^2=\frac{\pi d^2}{4}$

Putting all together:

$P=\frac{AV^2}{\rho L}=\frac{\pi d^2V^2}{4\rho L}$

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$P=\frac{\pi (0.00025m)^2(12V)^2}{4(1.68\times10^{-8}\Omega m)(10m)}=42.075W$

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