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3 years ago

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A man has a power of 90 W and mass 60 kg runs up a staircase in 40 s. If each staircase is 20cm high find the number of steps? (

physics grade 9- GRAVITATION)

1 answer:

34kurt3 years ago

4 0

I showed my working in the images above. if you have any questions please feel free to ask

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A piston-cylinder device contains Helium gas initially at 150 kPa, 20 o C, and 0.5m 3 . The helium is now compressed in a polytr

Molodets [167]

Answer:

Explanation:

Given

$P_1=150 kPa$

$T_1=20^{\circ}C$

$V_1=0.5 m^3$

$T_2=140^{\circ}C$

$P_2=400 kPa$

R for Helium $R=2.076$

$c_v=3.115 kJ/kg-K$

mass of gas $m=\frac{P_1V_1}{RT_1}$

$m=\frac{150\times 0.5}{2.076\times 293}$

$m=0.123 kg$

Similarly $V_2$ can be found

$\frac{P_1V_1}{T_1}=\frac{P_2V_2}{T_2}$

$V_2=0.264 m^3$

Work done $W=\int_{V_1}^{V_2}PdV$

$W=\frac{P_2V_2-P_1V_1}{n-1}$

$W=\frac{mR(T_2_T_1)}{n-1}$

Since it is a polytropic Process

therefore $PV^n=c$

$P_1V_1^n=P_2V_2^n$

$(\frac{V_1}{V_2})^n=\frac{P_2}{P_1}$

$(\frac{0.5}{0.264})^n=\frac{400}{150}$

$n=\frac{\ln 2.66}{\ln 1.893}$

$n=1.533$

$W=\frac{0.123\times 2.076(140-20)}{1.533-1}$

$W=57.48 kJ$

From Energy balance

$E_{in}-E_{out}=\Delta E_{system}$

Neglecting kinetic and Potential Energy change

$Q_{in}+W_{in}=change\ in\ Internal\ Energy$

Change in Internal Energy $\Delta U=u_2-u_1$

$\Delta U=mc_v(T_2-T_1)$

$\Delta U=0.123\times 3.115(140-20)$

$\Delta U=45.977 kJ$

$Q_{in}+57.48=45.977$

$Q_{in}=-11.50 kJ$

i.e. Heat is being removed

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3 years ago

When a customer in Japan was quoted a price of .39 cents a pound he thought he was being charged .39 a kilogram. He was shocked

Anon25 [30]

Answer: $85.80

Explanation: 100kg is equalvilent to 220 lbs, then you multiply 220 by .39 and then you have your answer :)

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3 years ago

Pick the correct answer

Marat540 [252]

The answer is A. Photosynthesis is caused when plants trap light energy in their leaves and use that energy to change water and carbon dioxide into glucose. Hope this helps :)

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3 years ago

Anyone knows how to do this? I think it’s 0 because it’s not moving————

dedylja [7]

Answer:

1 m/s

Explanation:

2 to 3 second interval would be zero.

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so average is 1 m/s

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Answer:

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