Study Guide on Work and Energy

There will be 20 multiple choice questions and 2 free response questions. Here are some sample free response questions.

Free Response Question # 1: A 6 kg concrete block is dropped from top of a tall building. The block has fallen a distance of 55 meters and has a speed of 30 meters per second when it hits the ground.

a) At the instant the block was released, what was its gravitational potential energy with respect to the ground? (Show all calculations, including the equation and substitution with units)PE=mgh=6kg(9.8 m/s2)(55m)=3234 J

b) Calculate the kinetic energy of the block at the point of impact. (Show all calculations, including the equation and substitution with units.)KE=1/2mv2=1/2(6kg)(30m/s)2=2700 J

c) How much mechanical energy was “lost” by the block as it fell?534 Jd) Using one or more complete sentences, explain what happened to the mechanical energy that

was “lost” by the block. Heat or Thermal Energy

Free Response Question # 2:

a) Using a metric ruler and the scale of 1 cm = 8 m, determine the height of the first hill2.5 cm= 20 m

b) Determine the gravitational potential energy of the car at the top of the first hill. (Show all calculations, including the equation and substitution with units.)PE=mgh=650 kg(9.8m/s2)(20 m)=127,400 J

c) Using one or more complete sentences, compare the kinetic energy at the top of the second hill to its kinetic energy at the top of the third hill.The kinetic energy of the car at the top of the third hill is greater than the kinetic energy at the top of the second hill.

Free Response Question # 3:

Name the forms of mechanical energy possessed by the system when the block is in position A and in position B.

Position A:___Kinetic Energy__________ Position B:__Elastic Potential Energy___________________

Free Response Question # 4:

a) Calculate the potential energy stored in the compressed spring. (Show all work including equations and substitutions with units.) PEs=1/2kx2=1/2(150 N/m)(0.05m)2=0.1875J

b) The toy is activated and all the compressed spring’s potential energy is converted into gravitational potential energy. Calculate the maximum vertical height to which the toy is propelled. (Show all work including equations and substitutions with units.)PE=mgh 0.1875J=(0.02 kg)(9.8m/s2)h h=0.96 m

Topics to Review:

1. Calculating work using W=Fd2. Calculating power using P=W/t=Fd/t=Fv3. Calculating work using the work-energy theorem4. Analyzing systems in which potential energy is converted into kinetic energy using conservation

of mechanical energy.5. Analyzing systems in which kinetic energy is converted into gravitational potential energy using

conservation of mechanical energy. Such systems include pendulums, spring mass systems, rollercoasters,etc. Remember KE = ½ mv2, PEg=mgh, and PEs=1/2 kx2

6. Be able to define, explain, and calculate internal energy (work done against friction, heat) in systems.

7. Be able to explain Hooke’s Law as it applies to elastic materials.

For additional test prep, see Castle Learning.