Kinetic & Potential Energy
What is the specific definition of Energy?
Ability to do work
What is the conservation of energy rule?
Energy cannot be created or destroyed; it can only be transferred or transformed.
What are the three necessary conditions for Work to be done on an object?
A force must act on the object, The object must move, The force must have a component in the direction of motion
What is power?
The rate at which work is done or energy is transferred.
A constant force of 25 Newtons pushes a cart across a flat floor for a distance of 8 meters. Calculate the work done on the cart.
200. W = F x D = 25 x 8
Gravitational potential energy depends on mass, gravity, and this third physical factor.
Height
On a roller coaster, where is the Kinetic Energy at its maximum and the Potential Energy at its minimum?
At the bottom of the track.
What is the unit for Work, and what is its definition in terms of Newtons and Meters?
The Joule (J). One Joule is a force of 1 Newton exerted over 1 meter.
A 100W lightbulb uses how much energy every second?
100 Joules. 1 Watt = 1 Joule/second
A 5 kg object possesses exactly 490 Joules of gravitational potential energy. Calculate the height of the object above the ground (use g=9.8).
h = 10. 490 = 5 x 9.8 x h = 49 x h. 490/49 = h = 10
If you take a moving object and triple its velocity while keeping its mass the same, by what specific factor does its kinetic energy increase?
9 because 3x3=9
What does the term wasted energy usually refer to in terms of transformations?
Energy converted into heat and sound due to friction.
Based on the Three Conditions rule, why is no work done if you push against a stationary wall?
Because there is no displacement (the object did not move).
Why are most machines not 100% efficient?
Energy is lost as heat due to friction or electrical resistance.
A machine does 6,000 Joules of work over a span of exactly 2 minutes. Calculate the power output of the machine in Watts.
w = 50. 6000 / 120 seconds = 50 W
A rubber band is stretched, and a heavy boulder is lifted to the top of a cliff. Name the two distinct types of potential energy represented in these scenarios.
Elastic potential energy (rubber band) and gravitational potential energy (boulder).
In real-world mechanical systems, total mechanical energy (kinetic + potential) appears to decrease over time. Explain why this happens without violating the Law of Conservation of Energy.
Friction and air resistance convert some of the mechanical energy into non-mechanical forms, like thermal energy and sound, which dissipate into the surroundings.
If force is applied to an object, explain how the angle of the force relative to the object's direction of motion affects the total amount of work.
Only the part that moves parallel to the direction of force does work. If the force is perfectly perpendicular to the motion, zero work is done.
What is the formula for calculating Efficiency?
(Useful Energy Out/Total Energy In)×100
If a motor has a total energy input of 1,000J but only 150J is useful energy, what is its efficiency?
15%
A car traveling at a certain speed slams on its brakes and skids to a halt. If the car had been traveling at twice that speed, how many times farther will it skid before coming to a complete stop, assuming the braking force remains the same?
4 times because 1/2 x m x (2v)² = 1/2 x m x 4v² meaning velocity changes 4x overall as 2² is 4
Track all the major energy transformations that occur from the moment a bungee jumper steps off a high platform until they reach the absolute lowest point of their fall.
Gravitational potential energy → Kinetic energy → Elastic potential energy (with some energy transforming into thermal energy due to air resistance and internal friction in the cord).
A satellite travels in a perfect circular orbit around Earth at a constant speed, held in place by gravity. Explain why gravity does exactly zero work on the satellite during its orbit.
The gravitational force acts perpendicular to the satellite's direction of motion at every point.
An engineer improves a vehicle's design, halving the amount of energy wasted as heat and sound, while keeping the total energy input the same. How does this effect useful energy output and its efficiency percentage?
Increases effect useful work output and its efficiency percentage
A machine applies a force of 300 Newtons to move an object a distance of 10 meters, completing the task in exactly 6 seconds. Calculate the power output of the machine in Watts.
500 watts. (300×10)/6 = 500