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3 years ago

A car traveling along the highway needs a certain amount of force exerted on it to stop it in a

Physics

2 answers:

erica [24]3 years ago

7 0

Answer:

More stopping force is required when the car has D) all of these.

Explanation:

Let's explain some equations and concepts in order to answer the question:

The second law of Newton states that a force exerted on an object is directly proportional to the mass of the object and the acceleration of the object.

Mathematically, we can write the following equation :

$F=m.a$ (I)

Where ''F'' is the force

Where ''m'' is the mass

And where ''a'' is the acceleration.

Now, we can define the momentum as :

$p=m.v$ (II)

The momentum ''p'' is a vector magnitude.

''m'' is the mass of the object

And ''v'' is the velocity vector.

Finally, let's explain the following motion equation :

$Vf=Vi-a.t$ (III)

Vf is final speed

Vi is initial speed

''a'' is the acceleration of the object.

Notice that we write a ''-'' in the ''a.t'' term because we assume that the object is stopping. Therefore, its acceleration is negative. ''t'' is the time in which the object will stop.

Let's proceed analyzing each option :

A) more mass

If the car has more mass, therefore by looking at the equation (I), the stopping force will be greater.

B) more momentum

By looking the equation (II), if the car has more momentum therefore it has more mass or more speed (or both).

If it has more mass the stopping force required must be greater.

Otherwise, if it has more speed, by looking at the equation (III) and assuming that Vf = 0 (because we need the car to stop) ⇒

$0=Vi-a.t$

$Vi=a.t$

If $Vi$ is greater and assuming that time must be the same, therefore the acceleration will be greater. So, if acceleration increases, the stopping force increases (looking at equation (I) ).

Finally, C) less stopping distance

If the car has less stopping distance, therefore the magnitude of the acceleration vector must be greater (in order to stop the car faster). By looking the equation (I) we conclude that the stopping force will be greater.

The correct option is D) all of these

sammy [17]3 years ago

3 0

A car traveling along the highway needs a certain amount of force exerted on it to stop it in a certain distance.

More stopping force is required when the car has more mass, or more momentum, or less stopping distance. (D)

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Expectant mothers many times see their unborn child for the first time during an ultrasonic examination. In ultrasonic imaging,

Rzqust [24]

A) A. 380 kHz

To clerly see the image of the fetus, the wavelength of the ultrasound must be 1/4 of the size of the fetus, therefore

$\lambda=\frac{1}{4}(1.6 cm)=0.4 cm=0.004 m$

The frequency of a wave is given by

$f=\frac{v}{\lambda}$

where

v is the speed of the wave

$\lambda$ is the wavelength

For the ultrasound wave in this problem, we have

v = 1500 m/s is the wave speed

$\lambda=0.004 m$ is the wavelength

So, the frequency is

$f=\frac{1500 m/s}{0.004 m}=3.75\cdot 10^5 Hz=375 kHz \sim 380 kHz$

B) B. f(c+v)/c−v

The formula for the Doppler effect is:

$f'=\frac{v\pm v_r}{v\pm v_s}f$

where

f' is the apparent frequency

v is the speed of the wave

$v_r$ is the velocity of the receiver (positive if the receiver is moving towards the source, negative if it is moving away from the source)

$v_s$ is the speed of the source (positive if the source is moving away from the receiver, negative if it is moving towards the receiver)

f is the original frequency

In this problem, we have two situations:

- at first, the ultrasound waves reach the blood cells (the receiver) which are moving towards the source with speed

$v_r = +v$ (positive)

- then, the reflected waves is "emitted" by the blood cells (the source) which are moving towards the source with speed

$v_s = -v$

also

v = c = speed of sound in the blood

So the formula becomes

$f'=\frac{c + v}{v - v_s}f$

C. A. The gel has a density similar to that of skin, so very little of the incident ultrasonic wave is lost by reflection

The reflection coefficient is

$R=\frac{(Z_1 -Z_2)^2}{(Z_1+Z_2)^2}$

where Z1 and Z2 are the acoustic impedances of the two mediums, and R represents the fraction of the wave that is reflected back. The acoustic impedance Z is directly proportional to the density of the medium, $\rho$ .

In order for the ultrasound to pass through the skin, Z1 and Z2 must be as close as possible: therefore, a gel with density similar to that of skin is applied, in order to make the two acoustic impedances Z1 and Z2 as close as possible, so that R becomes close to zero.

3 0

3 years ago

The current supplied by a battery slowly decreases as the battery runs down. Suppose that the current as a function of time is:

ludmilkaskok [199]

Answer: 8.1 x 10^24

Explanation:

I(t) = (0.6 A) e^(-t/6 hr)

I'll leave out units for neatness: I(t) = 0.6e^(-t/6)

If t is in seconds then since 1hr = 3600s: I(t) = 0.6e^(-t/(6 x 3600) ).

For neatness let k = 1/(6x3600) = 4.63x10^-5, then:

I(t) = 0.6e^(-kt)

Providing t is in seconds, total charge Q in coulombs is

Q= ∫ I(t).dt evaluated from t=0 to t=∞.

Q = ∫(0.6e^(-kt)

= (0.6/-k)e^(-kt) evaluated from t=0 to t=∞.

= -(0.6/k)[e^-∞ - e^-0]

= -0.6/k[0 - 1]

= 0.6/k

= 0.6/(4.63x10^-5)

= 12958 C

Since the magnitude of the charge on an electron = 1.6x10⁻¹⁹ C, the number of electrons is 12958/(1.6x10^-19) = 8.1x10^24 to two significant figures.

5 0

4 years ago

A stone is dropped from the edge of a roof. find the distance travelled by the stone in 2sec after its release.

Lena [83]

S = ?
U = 0
V = ?
A = 9.81
T = 2

we tryna find s

lets use s = ut + (at^2)/2
ut cancels out since u = 0
(at^2)/2 = (9.81 x 2^2)/2
= 19.62m

3 0

3 years ago

How does the use of biomass energy to create electricity harm the environment

EleoNora [17]

Biomass as an energy source is an alternative to fossil fuels (coal, petroleum, and natural gas). Burning either fossil fuels or biomass releases carbon dioxide (CO2), a greenhouse gas. However, the plants that are the source of biomass capture a nearly equivalent amount of CO2 through photosynthesis while they are growing, which can make biomass a carbon-neutral energy source.

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4 years ago

An audio amplifier provides an alternating rms emf of 15.0V a loudspeaker connected to the amplifier has a resistance of 10.4 w

Margarita [4]

Answer:

Current in the speaker will be 1.442 A

Explanation:

We have given an audio amplifier of rms emf of 15 volt

So emf of the audio amplifier $V=15volt$