Mechanical Energy & Work
Which of the following is a true statement?
Energy cannot be created or destroyed but only changed from one form to another.
Many science toys, such as the one show below, are marketed as perpetual motion machines.However, it is known that once set in motion, the balls will eventually stop moving. Why?
Friction and air resistance cause the balls to eventually stop moving.
Derek is running a race. As he approaches the finish line, he speeds up. How does this affect Derek's kinetic energy?
His kinetic energy increases.
A caveman wants to throw a rock off the cliff that will give it the greatest gravitational potential energy.Off of what cliff should the rock be thrown?
cliff 4 ( the highest one)
Energy flows through the environment in a variety of ways. All of the ways energy moves and is stored can be explained by the law of conservation of energy, which states that
energy cannot be created or destroyed, but it can be transformed into other kinds of energy.
There is a skier at the top of a ski slope. The skier has potential energy. What gives the skier his potential energy?
gravity
When mechanical energy is transformed,
heat is given off.
A refrigerator is a system. The energy input into the refrigerator system (in the form of electricity) is the same as the amount of energy output from the system. Which of the following best describes the energy output of the system?
heat, noise, and moving air
Nathan is building a deck out of 2 × 4 pieces of wood using sixteen penny nails. When swinging the hammer, the end of the hammer gains speed and
kinetic energy.
Suppose a stone is dropped from a high cliff. The stone's potential energy changes to kinetic energy as it falls. In reality, some energy is changed to thermal energy due to the friction of air resistance. Given this, the amount of time it would take the stone to fall in air (compared to in a vacuum) would be which of the following?
longer because the stone has less kinetic energy
At point A, Yurgi is sitting at the top of a sledding hill. At point B, Yurgi is moving down the hill at a velocity of 22 m/s.At which point does he have the most kinetic energy?
point B
Potential energy is best described as
stored energy.
Four balls were dropped from the same height. The balls and their masses are shown below.Which ball had the largest initial gravitational potential energy?
the baseball
Kinetic energy is best described as
the energy of motion
The gravitational potential energy of an object at a specific height is equal to
the work required to lift the object to that height.
Potential energy is dependent on
weight and height
Force times the distance traveled in the direction of that force is referred to as __________.
work
The picture below shows how the chemical energy in gasoline is transformed into the mechanical energy of a vehicle.
Yes; even though a lot of energy is converted into non-mechanical forms, all of the energy is accounted for.
Energy enables an object to do work. Work is done when
a force is put on an object, and the object moves in the direction of the force.
Sasha and Eric want to go sledding. Which of the following can give the sled enough energy to move?
a tall hill
Kinetic energy is the energy of motion. How could you determine how much kinetic energy an object has?
by finding its mass and speed
If a force of 16 newtons moves an object 7 meters, what is the work?
112 J
Work is defined as applied force acting through a distance, and it can be calculated according to the following formula: W = F x d where F is the force that is applied and d is the distance that an object moves in the direction of the applied force. In which of the following scenarios is the most work performed
A woman pushes a couch 2 meters across the floor with a force of 500 N.
Which of the following is a true statement about closed systems?
As kinetic energy increases, potential energy decreases.
How does friction affect the energy in a closed system of moving parts?
It converts some of the system's kinetic energy to thermal energy.
Jill is getting ready to push little Frank in his swing. She pulls Frank back as high as she can and then releases the swing. What is the initial transfer of energy that accelerates the swing when she lets go?
Potential energy is converted into kinetic energy.
Mark and Ann took a two-week hiking trip through Yosemite National Park. While hiking through the park, they witnessed two large blocks of rock break away from Glacier Point. What is the initial transfer of energy that accelerates the rock down the side of the mountain?
Potential energy is converted into kinetic energy.
Jake and Reuben are practicing for their weightlifting meet at school. Jake applies 800 newtons of force to the barbell and lifts it above his head. Reuben also applies 800 newtons of force to the same barbell, but he is a bit taller than Jake and has longer arms, so he lifts it farther above the ground. Which of the following statements is true?
Reuben did more work.
A truck and a car are traveling down the highway at the same speed. If the truck has a greater mass than the car, how do their kinetic energies compare?
The truck has more kinetic energy than the car.
Mac and Darnell work at a tire store. Their manager tells them to move some tires to a rack 1.5 meters above the ground. Mac takes 2 seconds to lift a tire from the ground to the rack. Darnell takes 4 seconds to move the same model of tire over the same distance. Which of the following statements is true?
They did the same amount of work.
