Potential & Kinetic Energy
This type of energy depends on an object's mass and its height above ground.
Gravitational potential energy
Name the six classical simple machines.
Lever, inclined plane, wedge, screw, wheel and axle, pulley.
Define work in physics terms (brief).
Work is the transfer of energy by a force acting over a distance in the same direction as the force.
Define mechanical advantage (MA).
The number of times a machine multiplies the input (effort) force.
A fixed pulley changes this about the applied force.
Direction (it changes direction but not the magnitude of force)
Write the formula for kinetic energy using mass m and velocity v.
KE=0.5×m×v2
A screw is a modified version of which simple machine?
An inclined plane
Calculate the work done moving a 50 N box 3 m across the floor in the direction of the force.
W=F×d=50×3=150 J
Provide the IMA formula using distances: IMA = (distance output) / (distance input).
IMA = distance (output) ÷ distance (input).
In a movable pulley attached to the load, the effort needed is typically: more, equal, or less?
Less (it reduces the needed input force).
If a rock is held higher above the ground, how does its gravitational potential energy change?
It increases.
Give two real-world examples of wedges.
Examples include knife blades and axe heads (other valid answers: nails, scissors cutting edge, shovel tip).
Define power and give its relationship to work and time.
Power is the rate of doing work; P=W/t
A ramp is 10 m long and raises a load 2 m. What is the IMA?
IMA = 10 ÷ 2 = 5
Identify which lever class this is: fulcrum at one end, load in middle, effort at other end.
Second-class lever
A 2 kg ball rolls at 3 m/s. Calculate its kinetic energy (show numeric final answer).
KE=0.5×2×32=9 J
Identify the three parts of a lever.
Fulcrum, effort (force), resistance (load).
Two students lift identical boxes the same height. Student A takes 4 s; Student B takes 2 s. Who did more power and by what factor?
Student B produced twice the power (same work in half the time)
A machine has 500 J input work and 420 J output work. Calculate efficiency (percent).
Efficiency = 420/500×100%=84%
Describe a block-and-tackle and its main benefit.
A system of multiple pulleys (fixed and movable) that provides increased mechanical advantage, reducing required effort.
Explain (briefly) how total mechanical energy changes if friction is present during motion.
Some mechanical energy is converted to thermal energy (heat) so total mechanical energy decreases while total energy is conserved.
Describe the mechanical advantage effect of a second-class lever compared to a third-class lever.
A second-class lever gives a mechanical advantage (effort arm longer than resistance arm) so it multiplies force; a third-class lever has effort between fulcrum and load and increases distance/speed rather than force.
A machine does 2000 J of work in 5 s. What is its power? Show calculation.
P=2000 J/5 s= 400 W
Explain why no machine can be 100% efficient in practical use.
Because some input energy is always converted to other forms (usually thermal energy) due to friction and other losses.
A wheel and axle has wheel radius 0.30 m and axle radius 0.05 m. If effort is applied to the wheel, what is the IMA (use radii)? Show calculation.
IMA = radius(wheel) ÷ radius(axle) = 0.30÷0.05=6