Transcript Document

WHICH OF THE FOLLOWING IS THE CORRECT
DEFINITION FOR WORK IN SCIENCE?
 A) How much your brain hurts after a test in Chem/Phys
 B) Where you go to make money
 C) The amount of force applied over a distance
WHICH OF THE FOLLOWING UNITS REPRESENT WORK?
 A) Newton
 B) Newton-meter
 C) Joule
 D) Meter
DRAW THE “WORK TRIANGLE”
PRACTICE PROBLEMS
 How much work is done on a 10 N block that is lifted 5 meters off the
ground by a pulley?
 Work = F x D
 F= 10N
 D= 5m
 10N X 5m = 50 J
PRACTICE PROBLEMS
 A woman lifts her 100 N child up 1 meter and carriers her for
a distance of 50 meters to her bedroom. How much work
does the woman do?
 100 N X 1 meter = 100J
PRACTICE PROBLEMS
 You pull your sled through the snow a distance of 500
meters with a force of 200 newtons. How much work
did you do?
 500 m X 200 N = 100,000J
PRACTICE PROBLEMS
 An ant sits on the back of a mouse. The mouse carries
the ant across the floor for a distance of 10 meters.
Was there work done by the mouse?
PRACTICE PROBLEM
 A force of 2000 N is applied to a machine in order to lift
a 1,000N load. What is the mechanical advantage of the
machine?
 2000N / 1000N = 2
PRACTICE PROBLEMS
 A large wind turbine is able to transform 1,500,000 J of
mechanical energy into 1,000,000 J of electrical energy every
second. What is the efficiency of this turbine?
 1,000,000 J / 1,500,000 J X 100 = 66%
PRACTICE PROBLEMS
 You did 170 J of work lifting a 140 N backpack.
How high did you lift the backpack?
 170J/140N = 1.2 m
PRACTICE PROBLEMS
 A crane does 62,500 J of work to lift a boulder a distance 25.0
m. How much did the boulder weigh?
 62,500J / 25.0 m = 2500 N
PRACTICE PROBLEMS
 An input force of 35 N is applied to a machine with a
mechanical advantage of 0.75. What is the size of the load this
machine could lift (how large is the output force)?
 0.75 X 35 N = 26.25N
PRACTICE PROBLEM
 If it requires 30 J of work to lift a bag of potatoes 2 m,
how much does the bag of potatoes weigh?
 30J / 2m = 15N
PRACTICE PROBLEM
 A 950 N skydiver jumps from a plane that is 3000m high. What
is the total work performed on the skydiver?
 950 N X 3000m = 2,850,000 J
PRACTICE PROBLEM
 A fern receives 1055J of light energy and through photosynthesis,
converts it to 8.3 J of energy to use for working plant system processes.
What is the efficiency of the fern?
 8.3J / 1055J X 100 = 0.8%