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koban [17]
3 years ago
8

A loaf of bread is removed from an oven at 350° F and cooled in a room whose temperature is 70° F. If the bread cools to 210° F

in 20 minutes, how much longer will it take the bread to cool to 185° F.
Physics
1 answer:
jasenka [17]3 years ago
7 0

Answer:

The bread will take 216.40 minutes to cool to 185°F

Explanation: Newton law of cooling

states that the rate of cooling of an object is inversely proportional to the difference of temperatures between the object and its surroundings i.e. dTdt=−kT, where t is the time taken and T is the difference of the temperatures between the object and its surroundings.

This gives us T as a function of t and is given by T(t)=ce−kt.

T(0)= Ce^-kt

C=35₩F- 185F= 165F

T(20) = 165×e^-20k=(350-70)

T(20)= e^-20k =280/165

-20k= ln(280/165)

-20k= ln(1.697)

-20k= 0.5289

K= 0.5289/20

K= 0.0264

If it cools at 185F in t minutes

165e^-0.0264×t=0.5

e^-0.0264t= 0.5/165

-0.0264t= on 3.03×10^-3

-0.0264t= -5.7129

t= 5.7129/0.0264

t=216.40minutes

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Answer:

a.52.9 km/h

b.90 km

Explanation:

We are given that

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t_1=30min

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t_2=12min

v_3=40km/h

t_3=45 min

Time spend on eating lunch and buying ga=15 min.

a.Total time=30+12+45+15=102 minute=\frac{102}{60}=1.7 hour

1 hour=60 minutes

Distance=speed\times time

d_1=v_1\times t_1=80\times\frac{30}{60}=40km

d_2=100\times \frac{12}{60}=20 km

d_3=40\times \frac{45}{60}=30 km

Total distance=d_1+d_2+d_3=40+20+30=90km

Average speed=\frac{total\;speed}{total\;time}

Using the formula

Average speed=\frac{90}{1.7}=52.9Km/h

b.Total distance between the initial and final city lies along the route=90 km

4 0
3 years ago
Find the frequency of a wave of wavelength 2.5m and speed 400 m/s
Sedaia [141]

Answer:

The frequency of wave is 160Hz.

Explanation:

Given that the formula of speed is V = f×λ where V represents speed, f is frequency and λ is wavelength.

So first thing, you have to make frequency the subject by dividing wavelength on both sides :

v = f \times λ \:

v \div  λ =  f \times λ \div λ

f =  \frac{v}{λ}

Next you have to substitute the value of v and f into the formula :

Let λ = 2.5m,

Let v = 400m/s,

f =  \frac{400}{2.5}

f = 160Hz

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DENIUS [597]
A) use v=u+at for both

First section, v=27, u=0, a=2.4. You should get 11seconds.
Second section, v=0, u=27, a=-1.3. You should get 21seconds.
This means that the total time is 22seconds.

b) You can either use s=ut+0.5at^2 or v^2=u^2+2as. Personally, I would use the second one as you are not relying on your previous answer.

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6 0
3 years ago
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