REGENTS PHYSICS         WORK AND ENERGY

MR. GAGNON                 REVIEW

 

1.) Two people of the same mass climb the same flight of stairs. The first person climbs the stairs in 25 seconds. The second person takes 35 seconds. Which person does the most work? Which person expends the most power? Explain your answers.

 

2.) A box that weighs 1000 Newtons is lifted a distance of 20.0 meters straight up by a rope and pulley system. The work is done in 10.0 seconds. What is the power developed in watts and kilowatts?

 

3.) A person of mass 64 kg climbs up a ladder to a height of 5.0 meters.

       a.) What work does the person do?

       b.) What is the increase in the gravitational potential energy of the

             person at this height?

       c.) Where does the energy come from to cause this increase in P.E.

 

4.) A 60.0 kg shell is shot from a cannon to a height of 400 meters.

       a.) What is the gravitational potential energy of the shell when it is

            at this height?

       b.) What is the change in potential energy of the shell when it falls to     a height of 100 meters?

 

5.) A person has a mass of 45 kg and is moving with a velocity of 10.0 m/s. a.) Find the personŐs kinetic energy.

       b.) The personŐs velocity becomes 5.0 m/s. What is the kinetic energy

            of the person?

       c.) What is the ratio of the kinetic energy in these two cases?

 

6.) A 15.0 kg object is moving with a velocity of 17.5 m/s. A force of -50.0 N acts on the object and its velocity becomes 3.20 m/s. What is the displacement of the object while the force acts?

 

7.) What type of energy does a wound watch spring possess? What form of energy does a running watch use? When the watch runs down, what has happened to the energy?

 

8.) A 15.0 kg model plane flies horizontally at 12.5 m/s.

       a.) Calculate its kinetic energy.

       b.) The plane goes into a dive and levels off 20.4 meters closer to the

            earth. How much potential energy did it lose during the dive?

       c.) How much kinetic energy did the plane gain during the dive?

       d.) What is its new kinetic energy?

       e.) Neglecting frictional effects, what is its new horizontal velocity?

 

9.) A partially filled bag of cement having a mass of 16.0 kg falls 40.0 meters into a river from a bridge.

       a.) What is the kinetic energy of of the bag as it hits the water?

       b.) Using energy considerations only, what vertical speed does it have?

 

10.) A 500 gram mass will stretch a given spring 65 cm. A student replaces the 500 gram mass with a 200 gram mass. She then pulls the mass 35 cm and releases it, setting the spring into motion.

       a.) What is the spring constant of the spring?

       b.) How much work does she do in stretching the spring?

       c.) Calculate the elastic potential energy.

       d.) How fast is the mass moving as it passes though the x = 0 position?