# Work, Power, and Energy Problems.

## Presentation on theme: "Work, Power, and Energy Problems."— Presentation transcript:

Work, Power, and Energy Problems

Amy uses 20N of force to push a lawn mower 10 meters
Amy uses 20N of force to push a lawn mower 10 meters. How much work does she do?

Amy uses 20N of force to push a lawn mower 10 meters
Amy uses 20N of force to push a lawn mower 10 meters. How much work does she do? W = F X D = 20 N X 10 M = 200 NM = 200 JOULES

Frank does 2400J of work in climbing a set of stairs that is 7 m high
Frank does 2400J of work in climbing a set of stairs that is 7 m high. What force does Frank exert when he climbs the stairs?

Frank does 2400J of work in climbing a set of stairs that is 7 m high
Frank does 2400J of work in climbing a set of stairs that is 7 m high. What force does Frank exert when he climbs the stairs? W = F X D = 2400 J = F X 7M F = 2400/7 = 343 NEWTONS

How much power is required to pull a sled if you use 60J of work in 5 seconds?

How much power is required to pull a sled if you use 60J of work in 5 seconds? POWER = W/T = 60/5 = 12 WATTS

How much work does an elephant do while moving a circus wagon 20 meters with a pulling force of 200N?

How much work does an elephant do while moving a circus wagon 20 meters with a pulling force of 200N? W = F X D = 200 X 20 = 4000 JOULES

If it takes 5 seconds for you to do 1000J of work, what is your power output?

If it takes 5 seconds for you to do 1000J of work, what is your power output? POWER = W/T = 1000/5 = 200 WATTS

A 900N mountain climber scales a 100m cliff
A 900N mountain climber scales a 100m cliff. How much work is done by the mountain climber?

A 900N mountain climber scales a 100m cliff
A 900N mountain climber scales a 100m cliff. How much work is done by the mountain climber? WORK = FORCE X DISTANCE = 900 N X 100 m = 90,000 watts

A small motor does 4000J of work in 20 seconds
A small motor does 4000J of work in 20 seconds. What is the power of the motor in watts?

A small motor does 4000J of work in 20 seconds
A small motor does 4000J of work in 20 seconds. What is the power of the motor in watts? POWER = WORK/TIME = 4000/20 = 200 WATTS

A woman runs a kilometer using a force of 210N and a power output of 500W. How long in minutes does it take this woman to complete 1 kilometer?

A woman runs a kilometer using a force of 210N and a power output of 500W. How long in minutes does it take this woman to complete 1 kilometer? WORK = FORCE X DISTANCE = 210 N X 1000m = 210,000 JOULES POWER = WORK/TIME TIME = WORK/POWER = 210,000/500 = 420 sec = 7 min

A toy cart moves with a kinetic energy of 30 J
A toy cart moves with a kinetic energy of 30 J. If its speed is doubled, what will its kinetic energy be? SINCE KE = ½ mv2 IF V IS DOUBLED, KE WILL INCREASE BY A FACTOR OF 4, SO KE = 120 J

A 70 kg diver is standing on a 10 m tower
A 70 kg diver is standing on a 10 m tower. What is the potential energy of the diver?

A 70 kg diver is standing on a 10 m tower
A 70 kg diver is standing on a 10 m tower. What is the potential energy of the diver? WEIGHT OF DIVER = 70 X 9.8 = 686 N PE = 686 X 10 = 6860 J

The 70 kg diver steps off the tower and falls into the water
The 70 kg diver steps off the tower and falls into the water. What is the kinetic energy of the diver? J

A 1300-kg car coasts on a horizontal road with a speed of 18 m/s
A 1300-kg car coasts on a horizontal road with a speed of 18 m/s. What is the kinetic energy of the car? KE = ½ mv2 = ½ x 1300 x (18) = J = KJ

When the 1300 kg car comes to a stop, what is its potential energy?

When the 1300 kg car comes to a stop, what is its potential energy
When the 1300 kg car comes to a stop, what is its potential energy? IT IS ON A HORIZONTAL ROAD. IT HAS NO HEIGHT ABOVE THE GROUND, SO THE POTENTIAL ENERGY IS ZERO.

What is the speed of a 3700 kg car if it has a kinetic energy of 118,400 J?

What is the speed of a 3700 kg car if it has a kinetic energy of 118,400 J? KE = ½ mv2 v2 = 2 x KE/m = 2 x / = 64 v = 8 m/s