Motion and Energy Transfer - Middle School Physical Science

1. What is kinetic energy in terms of mass and speed?

   $KE=\frac{1}{2}mv^2$. KE depends on mass and the square of velocity.

2. A car brakes to a stop on level ground; which energy transfer best links the motion change to energy?

   Kinetic energy transfers to thermal energy in brakes and tires. Friction in brakes converts motion energy to heat.

3. When an object falls (ignore air resistance), what energy conversion explains the speed increase?

   $GPE$ decreases and transfers to $KE$. Falling converts height energy to motion energy.

4. What is the definition of work as energy transfer by a force?

   Work is energy transferred when a force causes displacement. Force must move an object to transfer energy as work.

5. Which sign describes work by friction on a sliding object moving forward?

   Negative work. Friction opposes motion, doing negative work.

6. Which energy transfer is most directly associated with friction slowing an object?

   Kinetic energy is transferred to thermal energy. Friction converts motion energy into heat through molecular collisions.

7. As an object falls (ignoring air resistance), which energy change explains its speeding up?

   Gravitational potential energy transfers to kinetic energy. Gravity does positive work, converting height energy to motion.

8. Which energy transfer explains a stretched rubber band launching a projectile forward?

   Elastic potential energy transfers to kinetic energy. Stored elastic energy releases to accelerate the projectile.

9. What is the definition of energy transfer in a motion situation?

   Energy transfer is energy moving from one object or system to another. Energy cannot be created or destroyed, only moved between objects.

10. What is the definition of elastic potential energy in a stretched or compressed object?

    Stored energy due to deformation of an elastic object. Stretched/compressed materials store energy in molecular bonds.

11. What happens to kinetic energy when an object speeds up due to a push?

    Energy transfers into the object; $KE$ increases. Applied force does positive work, adding KE.

12. What happens to kinetic energy when mass doubles and speed stays constant?

    It becomes $2$ times larger. KE is directly proportional to mass when velocity is constant.

13. A $2\,kg$ cart speeds up from $3\,m/s$ to $5\,m/s$; what is $\Delta KE$?

    $16\,J$. $KE_f = \frac{1}{2}(2)(25) = 25J$, $KE_i = \frac{1}{2}(2)(9) = 9J$, so $\Delta KE = 16J$.

14. If a force does positive work on an object, how does the object's kinetic energy change?

    Kinetic energy increases. Positive work adds energy to the object's motion.

15. When an object is lifted at constant speed, what energy transfer occurs?

    Work transfers energy to increase $GPE$. Lifting does work against gravity, storing GPE.

16. A moving cart hits a spring and stops briefly; where is most of the cart's energy at that moment?

    Mostly stored as elastic potential energy in the spring. Compression stores the cart's kinetic energy in the spring.

17. A $3\,kg$ object is raised by $2\,m$; using $g\approx10\,m/s^2$, what is $\Delta GPE$?

    $60\,J$. $\Delta GPE = mgh = (3kg)(10m/s^2)(2m) = 60J$.

18. What energy transfer occurs when friction slows an object on a surface?

    Kinetic energy transfers to thermal energy. Friction converts motion energy to heat.

19. A ball is thrown upward; which energy transfer explains its slowing as it rises (ignore air resistance)?

    Kinetic energy transfers to gravitational potential energy. Gravity does negative work, converting motion to height energy.

20. State the formula for work when force and displacement are in the same direction.

    $W = Fd$. Work equals force times displacement when aligned.

21. What does positive net work on an object imply about its speed?

    Kinetic energy increases; speed increases. Positive work adds energy, increasing velocity.

22. What is gravitational potential energy near Earth in terms of height?

    $GPE=mgh$. GPE depends on mass, gravity, and height.

23. State the formula for gravitational potential energy using mass $m$, gravity $g$, and height $h$.

    $GPE = mgh$. GPE increases linearly with mass, gravity, and height.

24. What is the relationship between net work and change in kinetic energy?

    $W_{net}=\Delta KE$. Work-energy theorem: net work equals change in kinetic energy.

25. What does negative net work on an object imply about its speed?

    Kinetic energy decreases; speed decreases. Negative work removes energy, reducing velocity.

26. When a stretched rubber band launches an object, which energy transfer explains the motion?

    Elastic potential energy transfers to $KE$. Stored spring energy converts to motion energy.

27. What is the formula for kinetic energy of an object with mass $m$ and speed $v$?

    $KE = \frac{1}{2}mv^2$. Formula shows KE depends on mass and square of velocity.

28. A $10\,N$ push acts over $4\,m$ in the direction of motion; what work is done?

    $40\,J$. $W = Fd = (10N)(4m) = 40J$ when force is parallel to motion.

29. What happens to kinetic energy when speed doubles and mass stays constant?

    It becomes $4$ times larger. KE depends on $v^2$, so doubling $v$ gives $2^2 = 4$ times more energy.

30. Which statement best defines kinetic energy in terms of motion?

    Kinetic energy is the energy an object has because it is moving. Motion itself is the defining characteristic of kinetic energy.

31. In a collision where objects stick together, what happens to some of the initial kinetic energy?

    Some transfers to thermal energy, sound, and deformation. Inelastic collisions convert KE to other forms due to deformation.

32. Identify the energy transfer when brakes stop a bicycle wheel.

    Kinetic energy transfers to thermal energy. Brake friction converts motion to heat.

33. What is the formula for work done by a constant force parallel to motion?

    $W=Fd$. Work equals force times displacement when parallel.

34. If $W_{net}=30\,J$ on an object, what is $\Delta KE$?

    $30\,J$. By work-energy theorem, $\Delta KE$ equals net work done.

35. What is elastic potential energy for an ideal spring compressed or stretched by $x$?

    $E_{elastic}=\frac{1}{2}kx^2$. Elastic PE depends on spring constant and displacement squared.

36. If friction does negative work on a sliding object, what happens to the object's kinetic energy?

    Kinetic energy decreases. Negative work removes energy from the object's motion.

37. What is the definition of gravitational potential energy near Earth's surface?

    Stored energy due to height in a gravitational field. Objects at height can fall and gain kinetic energy.

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