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stepladder [879]

2 years ago

9

The width of a particular microwave oven is exactly right to support a standing-wave mode. Measurements of the temperature acros

s the oven show that there are cold spots at each edge of the oven and at three spots in between. The wavelength of the microwaves is 12 cm. a. How wide is the oven?
b. What is the frequency of the microwaves?

1 answer:

Tems11 [23]2 years ago

7 0

Answer:

a) l = 24 cm

b) υ = 2.5 × 10⁹ Hz

Explanation:

given,

wavelength of microwave = 12 cm

length of microwave

= 2 × λ

= 2 × 12

l = 24 cm

microwave is an electromagnetic wave speed is 3 × 10⁸ m/s

v = υ λ

υ = $\dfrac{v}{\lambda}$

υ = $\dfrac{3 \times 10^8}{0.12}$

υ = 2.5 × 10⁹ Hz

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A cord of negligible mass runs around two massless, frictionless pulleys. A canister with mass m = 20 kg hangs from one pulley.

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where T is the tension in the cord.

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Substituting into (2),

$F-mg = ma\\F=m(g+a)$

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As we said in part (a), the tension in the cord is equal to the force applied to the free end:

T = F

So

T = 196 N

Therefore, the work done by the tension is

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And since the force applied (F) is the same, then the work done by you when pulling the cord is exactly the same.

(d) -3.92 J

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$F_g = mg =(20 kg)(9.8 m/s^2)=196 N$

However, the direction of the force of gravity is opposite to the displacement. Therefore, the work done by gravity is negative:

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And substituting,

$W_g=-(196)(0.02)=-3.92 J$

(e) Zero

The net work done on the canister can be simply calculated by adding the work done by the tension in the cord and the weight of the canister:

$W=W_T+W_g = 3.92 + (-3.92 ) = 0$

This is in agreement with the work-energy theorem, which states that the work done on an object is equal to its change in kinetic energy. In this situation, the canister is moving at constant speed, so its kinetic energy is not change: therefore,

$\Delta K = 0$ (change in kinetic energy = 0)

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This is a simple pulley system, which means that the system does not multiply the force applied in input. In fact, the mechanical advantage of the system is

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TiliK225 [7]

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