Concept questions
False
If a person exerts 50,000 W of power over 25 seconds, how much work did the person do?
1250000 J
If someone increases the amount of time they do work on an object, will their power increase or decrease?
Decrease!
What type of simple machine is a see-saw?
First class lever
What two factors determine the work done on an object?
A boy pushes a car with a force of 200 N and the car doesn't move. How much work did the boy do?
A weightlifter presses a 400 N weight 0.5 meters over his head in 2 seconds. What is the power of the weightlifter?
100 W
What kind of simple machine is a lightbulb?
Screw
True or false: Power is the amount of force applied to an object multiplied by the amount of time it takes
False
Power = Work/Time
If someone increases the amount of time they do work on an object, will their work increase or decrease?
Time doesn't affect work so neither!
If a person exerts 2216.67 W of power over a span of 1.5 seconds to move an object 9.5 meters in the air, how much force did this person apply to the object?
350 N
What type of simple machine would be useful for lifting a pile of bricks up to the roof if repairs were needed on a house?
Pulley
If pulling a box across the ground with a rope, what forces are doing the work?
Tension and friction only
A bodybuilder is throwing a medicine ball in the air to work out. He tries to throw it about a distance of 5 meters above his head. If the mass of the medicine ball is 65 kg, and he throws it initially upward with an acceleration of 1.3 m/s², what is the work that this body builder does on the ball as he throws it?
422.5 J
Ms. Hogsten is demonstrating motion when he pushes a car across the parking lot causing it to accelerate. If Mr. Holbrook pushes with a force of 250 N, and moves the car 20 meters before stopping over 5 seconds, how much power did Ms. Hogsten exert?
1000 W
What type of simple machine would be useful during cooking?
Wedge
YES!
Mildred wants to test how powerful she is in comparison to her brothers by running up stairs. She has a mass of 60 kg. Her first brother Mark has a mass of 75 kg and her second brother Jessie has a mass of 55 kg. If the distance up the stairs is 2.5 meters, rank the siblings in terms of WORK.
Most to least:
Mildred > Mark > Jessie
Mildred wants to test how powerful she is in comparison to her brothers by running up stairs. She has a mass of 60 kg and runs up the stairs in 1.3 seconds. Her first brother Mark has a mass of 75 kg and runs up the stairs in in 1.9 seconds. Her second brother Jessie has a mass of 55 kg and runs up the stairs in 1.5 seconds. If the distance up the stairs is 2.5 meters, rank the siblings in terms of power and determine who is the most powerful among the siblings.
Most to least:
Mildred > Mark > Jessie
What type of simple machine is a steering wheel?
Wheel and Axle