9. Work & Energy

Intro to Energy & Kinetic Energy

Work and Energy


Both blocks will have the same final kinetic energy and the same final speed.



Block A will have a greater final kinetic energy and a greater final speed.



Block B will have a greater final kinetic energy and a greater final speed.



The blocks will have the same final kinetic energy, but block B will be moving faster.



The blocks will have the same final velocity, but block B will have greater kinetic energy.



The blocks will have the same final kinetic energy, but block A will be moving faster.


Block A has mass <math display="inline"><mrow><mn>20</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">kg</mi></mrow></math> and block B has mass <math display="inline"><mrow><mn>50</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">kg</mi></mrow></math>. Starting from rest, the two blocks are pushed by identical forces through a distance of <math display="inline"><mrow><mn>10</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">m</mi></mrow></math>. Which block (if either) is going faster at end of the <math display="inline"><mrow><mn>10</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">m</mi></mrow></math>? Which block (if either) has the greatest kinetic energy at the end of the <math display="inline"><mrow><mn>10</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">m</mi></mrow></math>?

What is the kinetic energy of a <math display="inline"><mrow><mn>500</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">kg</mi></mrow></math> car traveling at <math display="inline"><mrow><mn>27</mn><mo rspace="thickmathspace">&#x2062;</mo><mrow><mi mathvariant="normal" class="MathML-Unit">m</mi><mo>/</mo><mi mathvariant="normal" class="MathML-Unit">s</mi></mrow></mrow></math> (about <math display="inline"><mrow><mn>60</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">mph</mi></mrow></math>)?

About 50,000 years ago, a meteor crashed into the earth near present-day Flagstaff, Arizona. Some estimates suggest this meteor had a mass of about 1.4×108 kg and released 1×1016 J of energy when it slammed into the Earth. Calculate the approximate speed of this meteor before impact.

Kinetic Energy: Example Problems

At what speed does a 1000 kg compact car have the same kinetic energy as a 20,000 kg truck going 25 km/h?


A particle with mass m and velocity v has kinetic energy K. What is the kinetic energy of a particle with mass m/2 and velocity 2v?


A mother has four times the mass of her young son. Both are running with the same kinetic energy. What is the ratio v(son)/v(mother) of their speeds?

Intro to Energy & Types of Energy

Where does the kinetic energy formula come from?

(c) Is it reasonable that a 30-kg child could run fast enough to have 100 J of kinetic energy?

Energy | Physics with Professor Matt Anderson | M11-01

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1. Intro to Physics Units

2. 1D Motion / Kinematics

3. Vectors

4. 2D Kinematics

5. Projectile Motion

6. Intro to Forces (Dynamics)

7. Friction, Inclines, Systems

8. Centripetal Forces & Gravitation

10. Conservation of Energy

11. Momentum & Impulse

12. Rotational Kinematics

13. Rotational Inertia & Energy

14. Torque & Rotational Dynamics

15. Rotational Equilibrium

16. Angular Momentum

17. Periodic Motion

18. Waves & Sound

19. Fluid Mechanics

20. Heat and Temperature

21. Kinetic Theory of Ideal Gases

22. The First Law of Thermodynamics

23. The Second Law of Thermodynamics

24. Electric Force & Field; Gauss' Law

25. Electric Potential

26. Capacitors & Dielectrics

27. Resistors & DC Circuits

28. Magnetic Fields and Forces

29. Sources of Magnetic Field

30. Induction and Inductance

31. Alternating Current

32. Electromagnetic Waves

33. Geometric Optics

34. Wave Optics

36. Special Relativity

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