Energy accounting in open, closed and isolated systems

Answer Key - Grade 11 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   A motor does 250 J of work on a cart-and-track system, while 90 J of heat leaves it into the room. By how much does the system's energy grow, Ari?

   160 J
2. 2.

   A motor does 500 J of work on a cart-and-track system, while 320 J of heat leaves it into the room. By how much does the system's energy grow, Bo?

   180 J

3. Read this first

   Use this

   Energy bar chart (example data), one bar per energy store, height in J. Before: kinetic 0 J; thermal 0 J. After: kinetic 150 J; thermal 50 J. A transfer arrow goes from the motor to the cart and track, labeled work 200 J. A dashed system boundary surrounds the cart and the track. The motor is outside it; its work arrow crosses the boundary inward.

4. 3.

   In the energy bar chart, how much energy crosses the system boundary, Jun?

   • 200 J
   • 50 J
   • 150 J
5. 4.

   In the energy bar chart, how much of the motor's work ends up as thermal energy, Kira?

   • 50 J
   • 150 J
   • 200 J, the whole amount
6. 5.

   In the energy bar chart, why do the system's stores grow, Luz?

   • The track adds extra energy to the cart
   • Work from the motor crosses into the system
   • Energy is made inside the system
7. 6.

   A pot of soup simmers on a stove with no lid. Steam escapes and heat flows in. What kind of system is the soup, Milo?

   • Closed: energy crosses but matter does not
   • Open: matter and energy cross
   • Isolated: nothing crosses
8. 7.

   A sealed jar of water warms in the sun. What kind of system is the water in the jar, Noah?

   • Closed: energy crosses but matter does not
   • Open: matter and energy cross
   • Isolated: nothing crosses
9. 8.

   Two carts collide inside a sealed box. Treating the box as perfectly insulated, what kind of system is it, Pia?

   • Open: matter and energy cross
   • Isolated: nothing crosses
   • Closed: energy crosses but matter does not
10. 9.

    A box slides to a stop on a rough floor. Where did its kinetic energy go, Ren?

    • Into thermal energy in the box and floor
    • Into gravitational energy
    • It was destroyed
11. 10.

    A cart rolls to a stop on a carpet. What happened to the total energy of the cart, carpet and air, Tala?

    • It stayed the same
    • It grew, since the carpet warmed
    • It was used up