# Physics

posted by .

#1.) A wind turbine has a Cp of 0.42 and extracts 50 kW of power when the wind velocity is 25 m/sec. How long are the blades? (ρ = 1.2 kg/m3)

#2.) An electric hot water heater is used to heat 30 gallons of water from 20 °C to 45 °C.

a. What heat energy is required to increase its temperature?

b. What electric energy (still in Joules) is required if the efficiency is 98%?

c. If this heat energy flows into the water a constant rate over a 30 minute period, what power is
required over this period?

d. If this power is delivered by a resistive hot water heating element using a 240 V source, what must the resistance of the heating element be?

• Physics -

heattoheatwater=masswater*specific*(45-20)

figure mass water from volume and denstity, look up specific heat.

if eff is .98, then energy=heat/.98

power=heateneryg/timeinseconds

R=V^2/energy

## Similar Questions

1. ### English

1. He died young. 2. He died when he was young. 3. When he was young, he died. (Are they all the same?
2. ### College Physics

In Chapter 3 we learned that the force of air drag on an object moving rapidly through the air is proportional to v2, where v is the speed of the ball relative to the air. The same relation applies to the force of the wind on the blades …
3. ### Physics

A wind turbine is initially spinning at a constant angular speed. As the wind's strength gradually increases, the turbine experiences a constant angular acceleration of 0.180 rad/s2. After making 2874 revolutions, its angular speed …
4. ### algebra

Wind farms are a source of renewable energy found around the world. The power P(in kilowatts) generated by a wind turbine varies directly as the cube of the wind speed v(in meters per second) If a turbine generates 500kW in a 10m/s …
5. ### algebra

Wind farms are a source of renewable energy found around the world. The power P(in kilowatts) generated by a wind turbine varies directly as the cube of the wind speed v(in meters per second) If a turbine generates 700kW in a 5m.s …
6. ### physics

A wind turbine is initially spinning at a constant angular speed. As the wind's strength gradually increases, the turbine experiences a constant angular acceleration 0.170 rad/s2. After making 2870 revolutions, its angular speed is …
7. ### Physics

A wind turbine has blades that sweep an area of 2000m2. It converts the power available in the wind to electrical power with an efficiency of 50%. What is the electrical power generated if the wind speed is 10ms–1?
8. ### physics

an electric hot water heater takes in cold water at 13.0 degrees celsius and delivers hot water. the hot water has a constant temperature of 45 degrees celsius when the "hot" faucet is left open all the times, and the volume flow rate …
9. ### Algebra

The power P (in watts) generated by a windmill that has efficiency E is given by the formula P = 0.31ED^2V^3, where D is the diameter (in feet) of the windmill blades and V is the wind velocity (in ft/sec). Approximate the wind velocity …
10. ### Algebra2

Wind farms are a source of renewable energy found around the world. The power P (in kilowatts) generated by a wind turbine varies directly as the cube of the wind speed v (in meters per second). If a turbine generates 500kW in a 10m/s …

More Similar Questions