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3 years ago

What do you mean by negative acceleration? can an accelerating automobile starting from rest have a negative acceleration

Physics

1 answer:

Irina-Kira [14]3 years ago

4 0

Explanation:

The acceleration tells us how the speed changes per unit of time. If we say a body has a negative acceleration we are saying that its speed decreases over time.

If a body has a positive initial velocity and a negative acceleration: the velocity decreases. On the contrary, if the automobile has a negative initial velocity (in the opposite direction) and a negative acceleration: the velocity is increasing. Thus, an accelerating automobile starting from rest can have a negative acceleration.

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Three polarizing filters are shown in the figure below. The alignment of each filterâs transmission axis is shown, as measured f

lidiya [134]

Answer: B.

Explanation:

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2 years ago

A space vehicle accelerates uniformly from 85 m/s at t = 0 to 164 m/s at t = 10.0 s .How far did it move between t = 2.0 s and t

creativ13 [48]

First, we have a change in the velocity from 85 to 164 m/s in 10 sec.

Then, we calculate the <u>acceleration </u>as:

$a=\frac{v_{f}-v_{i} }{t} =\frac{164-85}{10}=7.9 m/s^2$

Hence we need to calculate the velocity of the space vehicle at t = 2 sec using the first equation of motion:

$v_{f}=v_{i}+at=85+7.9*2=100.8m/s$

Then, using the second equation of motion to calculate the distance:

$d=v_{i} t+\frac{1}{2}at^2$

$d=100.8*2+\frac{1}{2}*7.9*(2)^2=217.4m$

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3 years ago

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I think atoms and molecules in matter are always in motion because of kinetic energy.

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2 years ago

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You are falling off the edge.what should you do to avoid falling..?

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Determine the power that needs to besupplied by the fanifthe desired velocity is 0.05 m3/s and the cross-sectional area is 20 cm

Mariulka [41]

Answer:

A fan with an energy efficiency of 30 % would need 62.5 watts to bring a desired volume flow of 0.05 cubic meters per second through a cross-sectional area of 20 square centimeters.

Explanation:

Complete statement is: <em>Determine the power that needs to besupplied by the fan if the desired velocity is 0.05 cubic meters per second and the cross-sectional area is 20 square centimeters.</em>

From Thermodynamics and Fluid Mechanics we know that fans are devices that work at steady state which accelerate gases (i.e. air) with no changes in pressure. In this case, mechanical rotation energy is transformed into kinetic energy. If we include losses due to mechanical friction, the Principle of Energy Conservation presents the following equation:

$\eta\cdot \dot W = \dot K$

$\dot W = \frac{\dot K}{\eta}$ (Eq. 1)

Where:

$\eta$ - Efficiency of fan, dimensionless.

$\dot W$ - Electric power supplied fan, measured in watts.

$\dot K$ - Rate of change of kinetic energy of air in time, measured in watts.

From definition of kinetic energy, the equation above is now expanded:

$\dot W = \frac{\rho_{a}\cdot \dot V}{2\cdot \eta}\cdot \left(\frac{\dot V}{A_{s}} \right)^{2}$ (Eq. 2)

Where:

$\rho_{a}$ - Density of air, measured in kilograms per cubic meter.

$\dot V$ - Volume flow, measured in cubic meters per second.

$A_{s}$ - Cross-sectional area of fan, measured in square meters.

If we know that $\rho_{a} = 1.20\,\frac{kg}{m^{3}}$ , $\dot V = 0.05\,\frac{m^{3}}{s}$ , $\eta = 0.3$ and $A_{s} = 20\times 10^{-4}\,m^{2}$ , the power needed to be supplied by the fan is:

$\dot K = \left[\frac{\left(1.20\,\frac{kg}{m^{3}} \right)\cdot \left(0.05\,\frac{m^{3}}{s} \right)}{2\cdot (0.3)} \right]\cdot \left(\frac{0.05\,\frac{m^{3}}{s} }{20\times 10^{-4}\,m^{2}} \right)^{2}$

$\dot K = 62.5\,W$

A fan with an energy efficiency of 30 % would need 62.5 watts to bring a desired volume flow of 0.05 cubic meters per second through a cross-sectional area of 20 square centimeters.

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3 years ago