Work
What counts as work?
A. Holding a heavy box still
B. Pushing a cart forward across the floor
C. Pushing against a wall that does not move
B. Pushing a cart forward across the floor
What is power?
The rate at which work is done.
What is the purpose of using machines to do work?
To make work easier.
What is the formula for work?
W = Fd
What is the formula for power?
P = W/t
What is the formula for mechanical advantage?
MA = Fout/Fin
A student pushes a cart with 45 N of force for 6 m in the direction of the force.
How much work is done?
270 J
A person does 800 J of work in 10 seconds.
Calculate their power.
80 watts
A machine produces an output force of 240 N when a person applies 60 N of input force.
Calculate mechanical advantage.
4
A worker does 360 J of work moving a crate 9 m.
What force was applied in the direction of motion?
40 N
Student A does 600 J of work in 12 seconds.
Student B does 600 J in 6 seconds.
Who has greater power? Explain.
A = 50 W; B = 100 W. B does equal work in less time
A machine has a mechanical advantage of 5 and produces 350 N of output force.
What input force is needed?
70 N
An object is moved 2 m with a force of 0.35 N. How much work is done?
0.7 J
What is the unit for measuring power?
watts
A machine experiences increased friction.
What happens to its efficiency?
Why?
Efficiency decreases; more input energy is transferred into less useful forms