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3 years ago

14

Which of these correctly describes whether a girl holding a ball in the same position is doing work on the ball?

1 answer:

aksik [14]3 years ago

4 0

Answer:

The girl is doing work on the ball because the energy in her muscles changed, even though the ball is not displaced.

Explanation:

The complete question is...

Which of these correctly describes whether a girl holding a ball in the same position is doing work on the ball?

-The girl is doing work on the ball because the energy of the ball changed, even though it is not displaced.

-The girl is doing work on the ball because the energy in her muscles changed, even though the ball is not displaced.

-The girl is doing no work on the ball because the ball is not displaced.

-The girl is doing no work on the ball because she is exerting a net force on the ball.

Holding up a ball costs energy, which is used to counter the work that would have otherwise be done on the ball by gravity. Although no physical distance is moved, we should consider the fact that by holding the ball, the girls hand exerts physical force to hold the ball in place. Also, there is a potential gravitational work on the ball due to gravity, but the force exerted by the girls hand does an equivalent of this gravito-potential work in order to counter it and hold the ball in place. All these activities eventually lead to a change in energy in her hand muscle to show that energy is expended.

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Lonnie pitches a baseball of mass 0.20 kg. The ball arrives at home plate with a speed of 40 m/s and is batted straight back to

suter [353]

Answer:

B) 20N.s is the correct answer

Explanation:

The formula for the impulse is given as:

Impulse = change in momentum

Impulse = mass × change in speed

Impulse = m × ΔV

Given:

initial speed = 40m/s

Final speed = -60 m/s (Since the the ball will now move in the opposite direction after hitting the bat, the speed is negative)

mass = 0.20 kg

Thus, we have

Impulse = 0.20 × (40m/s - (-60)m/s)

Impulse = 0.20 × 100 = 20 kg-m/s or 20 N.s

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3 years ago

You want the current amplitude through a 0.450-mH inductor (part of the circuitry for a radio receiver) to be 1.90 mA when a sin

faust18 [17]

Answer:

Frequency required will be 2421.127 kHz

Explanation:

We have given inductance $L=0.450H=0.45\times 10^{-3}H$

Current in the inductor $i=1.90mA=1.90\times 10^{-3}A$

Voltage v = 13 volt

Inductive reactance of the circuit $X_l=\frac{v}{i}$

$X_l=\frac{13}{1.9\times 10^{-3}}=6842.10ohm$

We know that

$X_l=\omega L=2\pi fL$

$2\times 3.14\times f\times 0.45\times 10^{-3}=6842.10$

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3 years ago

A baseball is released at rest from the top of the Washington Monument. It hits the ground after falling for 6 s. What was the h

alukav5142 [94]

Answer:

Total height (s) = 176.4 m

Explanation:

Given:

Initial velocity (u) = 0 m/s

Time taken (t) = 6 sec

Acceleration due to gravity = 9.8 m/s²

Find:

Total height (s)

Computation:

s = ut + [1/2]gt²

s = (0)(6) + [1/2][9.8][6²]

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3 years ago

PE=30J, m=?, g=10m/s2, h=10m

OleMash [197]

Based on the given, this is probably a gravitational potential energy problem (PEgrav). The formula for PEgrav is:

PEgrav = mgh

Where:
m = mass (kg)
g = acceleration due to gravity
h = height (m)

With this formula you can derive the formula for your unknown, which is mass. First put in what you know and then solve for what you do not know.

$PEgrav=mgh$
$30J=m(10)(10[tex] \frac{30}{100} =m$ )[/tex]

Do operations that you can with what is given first.

$30J=m(100m)$

Transpose the 100 to the other side of the equation. Do not forget that when you transpose, you do the opposite operation.

$\frac{30}{100} =m$

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3 years ago

A soccer ball moving with an initial speed of 1.8 m/s is kicked with a

vova2212 [387]

Answer:

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Explanation:

Step 1: Given data

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Acceleration (a): 6.1 m/s²

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Step 2: Calculate the displacement (s) of the ball

The ball is moving with a uniformly accelerated rectilinear motion. We can calculate the displacement using the following suvat equation.

v² = u² + 2 × a × s

s = (v² - u²)/2 × a

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s = 7.0 m

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