11/2/09
Post date: Nov 02, 2009 3:12:20 AM
Bell Ringer: What is power?
Launch Rockets!
To turn in for rocket lab:
Why do we put water into the rockets (use what you know from chapter 9 to explain why rockets with water in them go higher and faster than rockets with only air)
Calculate the velocity at which the water exits the rocket.
Use the projectile motion equations from chapter 7 to find out the initial upward velocity of the rocket from the stand (dy=0, ay=-9.8m/s/s, t= ____, viy= ?)
Use the conservation of momentum equation to find the velocity of the water. Initial is before launch, when bottle and water are at rest on the launcher. Final is just after launch, as rocket flies up and water flies down. pi = pf. See photo 9 in the album below for a diagram.
Click here for the photos
Or here for the video.
Power
power = work / time, P = W/t
In SI, measured in Joules per second (J/s) or Watts (W)
Watts are small units, so kW is common (1 kW = 1000 Watts)
kWh (kilowatt-hour) is a unit of work (power x time), which is used to describe how much electricity an appliance or a house uses.
Electric bills
Reading an electric bill
In English, measured in horsepower (1 hp = 746 Watts)
How much does a 60 Watt light bulb cost for a year?
How much does a 15 Watt CFL cost for a year?
Page 203: 9-11, 12c, 12d