High School Physics : Energy

Example Questions

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Example Question #3 : Types Of Mechanical Energy

ball is about to roll off the edge of a  tall table. What is its current potential energy?

Explanation:

The equation for potential energy is . We are given the mass of the ball, the height of the table, and the acceleration of gravity in the question. The distance the ball travels is in the downward direction, making it negative.

Plug in the values, and solve for the potential energy.

The units for energy are Joules.

Example Question #4 : Types Of Mechanical Energy

A spring has a spring stiffness constant of .  How much must this spring be stretched to store  of potential energy?

Explanation:

Knowns

Unknowns

Equation

Plug in the vales and solve for the stretch of the spring.

Example Question #5 : Types Of Mechanical Energy

A car traveling at a velocity  can stop in a minimum distance .  What would be the car’s minimum stopping distance if it were traveling at a velocity of ?

Explanation:

Work causes a change in the kinetic energy of an object.  In the example of a car stopping, the work done on the car causes the car to slow down to a stop, therefore changing the kinetic energy.

Work is also equal to the force times the displacement of the object. In this case, we are assuming that the force applied to stop the car does not change.

Since the car is coming to a stop the final velocity of the car is 0m/s.

Therefore when you double the velocity, that value is then squared.

Therefore your kinetic energy is increased by  times the original amount.

If your kinetic energy is  times greater, than with the same force being applied, the stopping distance will also increase by  times since they are directly related.

Example Question #6 : Types Of Mechanical Energy

mass attached to the end of a spring causes it to stretch .  If another  mass is added to the spring, the potential energy of the spring will be

Twice as much

The same

3 times as much

4 times as much

Twice as much

Explanation:

Hooke’s law states that spring constant is directly related to the force applied and the distance that the object is stretched.

We also know that the potential energy of a spring is related to the spring constant and the distance that the object is stretched

We can substitute our equation for Hooke’s law into the potential energy equation.

This simplifies to

This equation shows that there is a direct relationship between the force on the spring and the potential energy of the spring.  If the force is doubled, then the potential energy will likewise double.

Example Question #7 : Types Of Mechanical Energy

A spring with  hangs vertically next to a ruler.  The end of the spring is next to the  mark on the ruler.  If a  mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?

Explanation:

Known

Unknown

First let us consider the force acting on the spring. Since the spring is hanging vertically, the only force acting on the spring is the force of gravity from the mass that has been added to the spring.

We can substitute in our variables and find the gravitational force.

According to Hooke’s Law the spring constant of a spring is directly proportional to the force acting on it and inversely proportional to the amount of stretch.

We can use the provided spring constant and the force acting on the spring to determine the amount of stretch.

Example Question #8 : Types Of Mechanical Energy

A baseball has a mass of . If a high school pitcher can throw a baseball at , what is the approximate kinetic energy associated with this pitch?

Explanation:

To solve for the kinetic energy, we will need to use the equation:

Before we can plug in our given values, we must convert the mass from grams to kilograms. Remember, the SI unit for mass is kilograms, so most calculations will require this conversion.

Now we can use this mass and the given velocity to solve for the kinetic energy.

Example Question #9 : Types Of Mechanical Energy

When the speed of your car is doubled, by what factor does its kinetic energy increase?

Explanation:

Therefore when you double the velocity, that value is then squared.

Therefore your kinetic energy is increased by 4 times the original amount.

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