Use position, force and energy to answer different questions about the same system.
Start with the quantity you are asked to find
A cart at 4 m moves to 10 m and later returns to 6 m. Its path adds 6 and 4 m. The signed displacement compares 6 with 4 m. Neither tells you the acceleration without information about how velocity changes or what forces act.
For a one-dimensional force calculation, pick one positive direction. A cart moving left with a rightward net force has rightward acceleration. Initially that can reduce its speed; whether it later reverses depends on how long the force acts.
Mark the energy boundary
In a model that includes a cart and its rough track, friction can reduce the cart’s mechanical energy while heating surfaces inside the system. Moving the boundary to the cart alone changes what may cross it. Keep the same boundary throughout your explanation.
Power and energy answer different questions. A machine that delivers 80 J in 2 seconds transfers 40 J per second on average. A second machine that delivers the same work in 4 seconds transfers 20 J per second. Neither work rate, by itself, gives efficiency.
Apply the guide
A cart moves east while the net force is west. Is its acceleration east because it is moving east?Reveal explanation
No. Its acceleration is west, in the direction of the net force.
A sled and track lose 7 J of mechanical energy in a nearly isolated model. Where does the 7 J go?Reveal explanation
It is accounted for by other forms inside the chosen system, such as thermal energy.
Turn the idea into practice.
Apply the rule to a new case, then explain your choice.
Practice this skillSources & authorship
Sources support scientific principles. Practice scenarios and teaching examples are original.
Original OpenExam guide
Independent educator review is pending. This guide is not an official exam paper or a video transcript.
OpenStax Physics 4.3 Newton's Second LawOpenStax Physics 9.2 Mechanical Energy and Conservation of EnergyOpenStax Physics 2.1 Relative Motion Distance and DisplacementOpenStax Physics 9.1 Work Power and the Work–Energy Theorem