Try It

Complete the KE and PE calculation example problems in the tabs below. Read the scenario and complete the problem in your notebook. Be sure to identify the known and unknown values, write out the formula you are using, and show your work. Then, progress to the next tab to check your answer.


Problem 1

The gravitational potential energy of a 13 kg object is 290 joules. What is the height of the object above the ground?



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Answer to Problem 1

Problem 1: The gravitational potential energy of a 13 kg object is 290 joules. What is the height of the object above the ground?


Answer:

  1. Identify the known and unknown values.

    PE = 290 J

    m = 13 kg

    g = 9.8 m/s2

    h = ?


  2. Identify the formula you need to use to find the unknown value.

    PE = mgh


  3. Reconfigure the formula so that the unknown value you are solving for is one side of the equation by itself.

    PE = mgh

    Divide both sides by mg to get h on one side.

    h = PE / mg


  4. Input your known values into the formula and solve.

    h = PE / mg

    h = 290 J / (13 kg)(9.8 m/s2)

    h = 2.3 m


  5. Answer: The object is 2.3 meters above the ground.


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Problem 2

Lanie is riding her bicycle. The combined mass of the bicycle and Lanie is 100 kilograms are traveling at a speed of 7 meters per second. What is the kinetic energy of the bicycle and rider?



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Answer to Problem 2

Problem 2: Lanie is riding her bicycle. The combined mass of the bicycle and Lanie is 100 kilograms are traveling at a speed of 7 meters per second. What is the kinetic energy of the bicycle and rider?


Answer:

  1. First, identify the known and unknown values.

    m = 100 kg

    v = 7 m/s

    KE = ?


  2. Identify the formula you need to use to find the unknown value.

    KE = 1/2 mv2


  3. Input your known values into the formula and solve.

    KE = 1/2 mv2

    KE = 1/2 (100 kg)(7 m/s2)2

    KE = 2450 J


  4. Answer: The kinetic energy of Lanie and the bike is 2450 J.


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Problem 3

The kinetic energy of a bowling ball traveling at a speed of 4.2 m/s is 55 J. What is the mass of the bowling ball?



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Answer to Problem 3

Problem 3: The kinetic energy of a bowling ball traveling at a speed of 4.2 m/s is 55 J. What is the mass of the bowling ball?


Answer:

  1. First, identify the known and unknown values.

    v = 4.2 m/s

    KE = 55 J

    m = ?


  2. Identify the formula you need to use to find the unknown value.

    KE = 1/2 mv2


  3. Reconfigure the formula so that the unknown value you are solving for is one side of the equation by itself.

    KE = 1/2 mv2

    Multiply both sides by 2.

    2 (KE) = (1/2 mv2) (2)

    2 (KE) = mv2

    Divide both sides by v2.

    2 (KE) / (v2) = m

    Now, we have m isolated on one side of the equation.

    m = 2 KE / (v2)


  4. Input your known values into the formula and solve.

    m = 2 KE / (v2)

    m = 2 (55 J) / (4.2 m/s)2

    m = 110 J / (17.64 m2/s2)

    m = 6.24 kg


  5. Answer: The mass of the bowling ball is 6.24 kg.


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