Try this at home!

Water that won't boil!

St. Mary's H.S. Physics YouTube Channel

School Blocks YouTube? Download file below

Bouncing_Water_Drops.mov

 

 

 

 

Turning which gear would give you
a mechanical advantage?

ETC Clipart

William Dwight Whitney The Century Dictionary and Cyclopedia: An encyclopedic Lexicon of the English Language. (New York: The Century Co., 1889)4499
Copyright: 2009, Florida Center for Instructional Technology. See license.

 

 

 

Small Gear

 

C) Power - rate of doing work or expending energy

 

 

P = W/t = Fd/t =  Fv
(watt)   = (J/s)   (N)m/s    

 

Scalar

 

1 Horse Power = 746 Watts

 

 

 

Ex 1) 1440 kg car accelerates from rest to 95 km/hr in 7.4 sec.
What average power is used?

 

P = W/t

 

P = DKE/t

 = 1/2m(V22 - V12)/t

Convert km/hr

95 km/hr[1000m/km][hr/3600sec]

 

 

6.6 x 104 W or 88 hp

 

1 Horse Power = 746 Watts

 

 

P = W/t = Fd/t =  Fv
(watt)   = (J/s)   (N)m/s    

 

 

 

 

 

 

Ex 2) A 95 kg football player runs up stairs in 66s. The stairs are 140 m long at an angle of 32°

 

Her power output vertically is

 

 

P = W/t

 

P = Fd/t

 

F = [mgsinq]d/t

 

 

P = 1047 W

P = 1.0 x 103 W

P = W/t = Fd/t =  Fv
(watt)   = (J/s)   (N)m/s    

 

 

P = Fd/t

 

 

 

 

 

Ex 3)  1200 kg car has a max. power output of 120 hp. How steep a hill can it climb at constant speed of 75 km/hr if the frictional force is 650 N?

v=75 km/hr[1000m/km][hr/3600s]

v = 21 m/s

P = Fv

1 Horse Power = 746 Watts

P = 746 W[120 hp]

P = 9.0 x 105 W

At constant speed a = 0

Fnet = -mgsinq - f + Fcar = 0

 

 Fcar = mgsinq + f   

 

P = Fv

 

 P = [mgsinq + f]v  

 

 

= 18°

 

P = W/t = Fd/t =  Fv
(watt)   = (J/s)   (N)m/s    

 

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