Name ______
Unit 10 Notes: Work, Power, and Energy
An object’s ability to produce a change in itself or its environment is called ______.
A moving object has ______.
The relationship between doing work and a resulting change in energy was established by physicist ______.
When a force moves an object through a distance, ______is done.
When lifting an object, the force = ______.
- A 105 gram hockey puck is sliding across the ice. A player exerts a constant 4.5 N force over a distance of 0.15 m. How much work does the player do on the puck?
- If the hockey player lifts the puck a distance of 1.8 m, how much work has been done?
- A forklift raises a box 1.2 m doing 7 kJ of work on it. What is the mass of the box?
A force exerted ______to the motion does no work. As Mrs. Morgan carries a book across the room, her ______do the work.
If an object is moving horizontally, only use the ______of the force if it is being applied at an angle.
- A sailor pulls a boat 30 m along a dock using a rope that makes a 25o angle with the horizontal. How much work does the sailor do on the boat if he exerts a force of 255 N on the rope?
- A rope is used to pull a metal box 15 m across the floor. The rope is held at an angle of 46o with the floor and a force of 628 N is used. How much work does the force on the rope do?
______is the rate of doing work. The faster you do work, the more powerful you are.
- An electric motor lifts an elevator 9 m in 15 s by exerting an upward force of 12000 N. What power does the motor produce in watts and kilowatts?
- A motor’s power is 65 kW, and it lifts an elevator 17.5 m in 35 s. How much force does the motor exert?
Some objects have energy because they are in motion. This is called ______.
- An 875 kg car speeds up from 22 m/s to 44 m/s while passing another car. What were its initial and final kinetic energies, and how much work was done on the car to increase its speed?
Some objects have energy because of their ______. They have the potential to fall, so this energy is called
______.
- A 2 kg textbook is sitting on a shelf that is 2.1 m above the floor. What is its gravitational potential energy?
- If the textbook falls, what is its kinetic energy the instant before hitting the floor?
Energy can change forms, but the total amount remains constant in a closed system:
- A large chunk of ice with mass 15 kg falls from a roof 8 m above the ground.
- What is the kinetic energy of the ice when it reaches the ground?
- How fast is it going when it reaches the ground?
If no kinetic energy is lost during a collision, it is ______.
If some the kinetic energy is lost, a collision is ______.
This happens when energy is lost in the form of heat or sound to the environment.
Other types of potential energy:
When you stretch of compress a spring, ______is done. If work is done, then ______is transferred. The energy stored in the spring is called ______.
______: the more you stretch or compress a spring, the more force you must use.
The ______is a measure of how easily a spring stretches. It tells you how many Newtons of force are needed to stretch a spring each meter, cm, mm, inch, etc.
To calculate the energy stored in a spring:
- A spring has a spring constant of 440 N/m. How much must this spring be stretched to store 25 J of potential energy?
- How much force must you apply to stretch this spring 4.5 m?