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4 years ago

13

A person does 50j of work to lift a crate using a pulley. The plley's work output is 42j. What is the pulleys mechanical efficie

ncy?

1 answer:

ruslelena [56]4 years ago

8 0

(42/50)*100=84%

Because efficiency =(Useful/total)*100

Hope this helps!

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Draw a ray diagram for a diverging lens that has a focal length of -10 cm when an object is placed 30 cm from the lens's surface

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Explanation:

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2 years ago

What type of device forms images through refraction?

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Explanation:

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A batted ball is fair if it hits third base. *<br> True<br> O O<br> False

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3 years ago

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A baseball team is practicing throwing balls vertically upward to test their throwing arms. A player manages to throw a ball tha

Nitella [24]

We can solve this problem using the law of conservation of energy.
This law states that energy in a closed system must stay same.
That means that the energy of a ball leaving the hand and the energy of a ball when it reaches its maximum height must be the same.
The energy of a ball leaving the players hand is kinetic energy:
$E_k=\frac{mv^2}{2}$
The energy when the ball reaches its maximum height ( and has zero velocity) is potential energy in a gravitational field:
$E_p=mgh$
As said before these energies must be the same, and that allows us to find the initial speed:
$E_k=E_p\\
\frac{mv^2}{2}=mgh\\
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3 years ago

A vacuum cleaner produces sound with a measured sound level of 75.0 dB. (a) What is the intensity of this sound in W/m2? W/m2 (b

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Answer:

Part a)

$I = 3.16 \times 10^{-5} W/m^2$

Part b)

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Explanation:

Part a)

Level of sound = 75 dB

now we know that

$L = 10 Log\frac{I}{I_0}$

here we know that

$I_0 = 10^{-12} W/m^2$

now we have

$75 = 10 Log(\frac{I}{10^{-12}})$

$I = 3.16 \times 10^{-5} W/m^2$

Part b)

Intensity of sound wave is given as

$I = \frac{1}{2}\rho A^2\omega^2 c$

here we know that

$A = \frac{P_o}{Bk}$

so we have

$I = \frac{1}{2}\rho(\frac{P_o}{Bk})^2\omega^2 c$

$I = \frac{1}{2}\rho P_o^2 \frac{c^3}{B^2}$

now we know

$\rho = 1.2 kg/m^3$

$c = 340 m/s$

$B = 1.4 \times 10^5 Pa$

now we have

$3.16 \times 10^{-5} = \frac{1}{2}(1.2)P_o^2\frac{340^3}{(1.4\times 10^5)^2}$

$P_o = 0.162 Pa$

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3 years ago