Question

Qualitative practice with systems

For the following situations, determine whether the energy of the given system is the same at the initial and final states indicated (i.e., is the energy of the system constant or not).

0pts
0pts

A block is hung from a spring that is vertical and connected to the ceiling. The block is made to oscillate vertically. Call the initial state when the block is at its highest position and the final state when the block is at its equilibrium position.
Energy of the system is constant Energy of the system is not constant  System: block
Energy of the system is constant Energy of the system is not constant  System: block + ceiling (+ spring) + Earth
Energy of the system is constant Energy of the system is not constant  System: block + Earth

A block on a table (friction between the table and the block is not negligible) is attached to a wall via a spring that is horizontal. You give the block a brief push so that the block travels horizontally. Call the initial state when the spring first reaches its maximum stretch in the initial direction of motion. The final state is when the spring first reaches its zero stretch length.
Energy of the system is constant Energy of the system is not constant  System: block + wall (+ spring) + table
Energy of the system is constant Energy of the system is not constant  System: block + wall (+ spring)
Energy of the system is constant Energy of the system is not constant  System: block + table
Energy of the system is constant Energy of the system is not constant  System: table
Energy of the system is constant Energy of the system is not constant  System: block

1pts

Qualitative practice with systems For the following situations, determine whether the energy of the given system is the same at the initial and final states indicated (i.e., is the energy of the system constant or not). 0pts 0pts A block is hung from a spring that is vertical and connected to the ceiling. The block is made to oscillate vertically. Call the initial state when the block is at its highest position and the final state when the block is at its equilibrium position. Energy of the system is constant Energy of the system is not constant  System: block Energy of the system is constant Energy of the system is not constant  System: block + ceiling (+ spring) + Earth Energy of the system is constant Energy of the system is not constant  System: block + Earth A block on a table (friction between the table and the block is not negligible) is attached to a wall via a spring that is horizontal. You give the block a brief push so that the block travels horizontally. Call the initial state when the spring first reaches its maximum stretch in the initial direction of motion. The final state is when the spring first reaches its zero stretch length. Energy of the system is constant Energy of the system is not constant  System: block + wall (+ spring) + table Energy of the system is constant Energy of the system is not constant  System: block + wall (+ spring) Energy of the system is constant Energy of the system is not constant  System: block + table Energy of the system is constant Energy of the system is not constant  System: table Energy of the system is constant Energy of the system is not constant  System: block 1pts Incorrect. Tries 2/15 Previous Tries 0pts A person wearing roller skates is standing in front of a wall. Assume that the wheels on the skates are good enough that they roll ideally. The person pushes off the wall and begins traveling away from the wall. Call the initial state when the person was standing at rest in front of the wall with her hand touching the wall. The final state is when she has traveled 2 m away from the wall and is moving at a constant speed of 0.69 m/s. Energy of the system is constant Energy of the system is not constant  System: girl+wall Energy of the system is constant Energy of the system is not constant  System: wall Energy of the system is constant Energy of the system is not constant  System: girl A person is jumping on a trampoline. After coming off of the trampoline, he is in the air for 1.4 seconds. Call the initial state when the trampoline is at its lowest point with the person still on the trampoline. The final state is 0.8 seconds after the person comes off the trampoline. Energy of the system is constant Energy of the system is not constant  System: girl + Earth Energy of the system is constant Energy of the system is not constant  System: trampoline Energy of the system is constant Energy of the system is not constant  System: girl Energy of the system is constant Energy of the system is not constant  System: girl + trampoline Energy of the system is constant Energy of the system is not constant  System: girl + trampoline + Earth 1pts Tries 0/15 You push a box up a ramp (friction between the box and the ramp is not negligible). Call the initial state when you begin to push the box. Call the final state after you have pushed the box up the ramp a distance of 0.5 m and it is moving with a speed of 2 m/s Energy of the system is constant Energy of the system is not constant  System: you Energy of the system is constant Energy of the system is not constant  System: box + ramp + Earth + you Energy of the system is constant Energy of the system is not constant  System: box + ramp Energy of the system is constant Energy of the system is not constant  System: box + ramp + Earth Energy of the system is constant Energy of the system is not constant  System: box Two cars are driving down the road. They notice that they are going to crash, so both drivers slam on the brakes. The cars skid, but still collide. The cars stick together and eventually slide to a stop. Call the initial state just before the drivers apply the brakes and the final state just after the collision had occurred. Treat this situation as realistically as possible. Energy of the system is constant Energy of the system is not constant  System: the first car Energy of the system is constant Energy of the system is not constant  System: both cars Energy of the system is constant Energy of the system is not constant  System: the second car Energy of the system is constant Energy of the system is not constant  System: both cars + the ground 1pts

0pts

A person wearing roller skates is standing in front of a wall. Assume that the wheels on the skates are good enough that they roll ideally. The person pushes off the wall and begins traveling away from the wall. Call the initial state when the person was standing at rest in front of the wall with her hand touching the wall. The final state is when she has traveled 2 m away from the wall and is moving at a constant speed of 0.69 m/s.
Energy of the system is constant Energy of the system is not constant  System: girl+wall
Energy of the system is constant Energy of the system is not constant  System: wall
Energy of the system is constant Energy of the system is not constant  System: girl

A person is jumping on a trampoline. After coming off of the trampoline, he is in the air for 1.4 seconds. Call the initial state when the trampoline is at its lowest point with the person still on the trampoline. The final state is 0.8 seconds after the person comes off the trampoline.
Energy of the system is constant Energy of the system is not constant  System: girl + Earth
Energy of the system is constant Energy of the system is not constant  System: trampoline
Energy of the system is constant Energy of the system is not constant  System: girl
Energy of the system is constant Energy of the system is not constant  System: girl + trampoline
Energy of the system is constant Energy of the system is not constant  System: girl + trampoline + Earth

1pts

Tries 0/15

You push a box up a ramp (friction between the box and the ramp is not negligible). Call the initial state when you begin to push the box. Call the final state after you have pushed the box up the ramp a distance of 0.5 m and it is moving with a speed of 2 m/s
Energy of the system is constant Energy of the system is not constant  System: you
Energy of the system is constant Energy of the system is not constant  System: box + ramp + Earth + you
Energy of the system is constant Energy of the system is not constant  System: box + ramp
Energy of the system is constant Energy of the system is not constant  System: box + ramp + Earth
Energy of the system is constant Energy of the system is not constant  System: box

Two cars are driving down the road. They notice that they are going to crash, so both drivers slam on the brakes. The cars skid, but still collide. The cars stick together and eventually slide to a stop. Call the initial state just before the drivers apply the brakes and the final state just after the collision had occurred. Treat this situation as realistically as possible.
Energy of the system is constant Energy of the system is not constant  System: the first car
Energy of the system is constant Energy of the system is not constant  System: both cars
Energy of the system is constant Energy of the system is not constant  System: the second car
Energy of the system is constant Energy of the system is not constant  System: both cars + the ground

Answer 1

FIRST FOUR QUESTIONS AS PER THE RULES........PLEASE FOLLOW THE RULES

_________________________________

A block is hung from a spring that is vertical and connected to the ceiling. The block is made to oscillate vertically. Call the initial state when the block is at its highest position and the final state when the block is at its equilibrium position.

Reasoning - Any dissipated energy will be in earth, so energy will be constant for a system where earth is considered too. Otherwise it is not constant.

Energy of the system is not constant, System: block
Energy of the system is constant , System: block + ceiling (+ spring) + Earth
Energy of the system is not constant  System: block + Earth

_____________________________________________________

A block on a table (friction between the table and the block is not negligible) is attached to a wall via a spring that is horizontal. You give the block a brief push so that the block travels horizontally. Call the initial state when the spring first reaches its maximum stretch in the initial direction of motion. The final state is when the spring first reaches its zero stretch length.

Reasoning - friction is not negligible so energy stored in spring is dissipated as heat

Energy of the system is constant System: block + wall (+ spring) + table
Energy of the system is not constant  System: block + wall (+ spring)
Energy of the system is not constant  System: block + table
Energy of the system is not constant  System: table
Energy of the system is not constant System: block

_____________________________________________________________

A person wearing roller skates is standing in front of a wall. Assume that the wheels on the skates are good enough that they roll ideally. The person pushes off the wall and begins traveling away from the wall. Call the initial state when the person was standing at rest in front of the wall with her hand touching the wall. The final state is when she has traveled 2 m away from the wall and is moving at a constant speed of 0.69 m/s.

Reasoning - assuming there is no energy transfer into thermal energy due to friction

Energy of the system is constant, System: girl+wall

Energy of the system is constant System: wall

Energy of the system is constant System: girl

_____________________________________________________________

A person is jumping on a trampoline. After coming off of the trampoline, he is in the air for 1.4 seconds. Call the initial state when the trampoline is at its lowest point with the person still on the trampoline. The final state is 0.8 seconds after the person comes off the trampoline.

Reasoning - when we consider the whole system of girl + trampoline, then energy is dissipated, so it is not conserved. Energy is conserved when we consider earth too.

Energy of the system is not constant  System: girl + Earth
Energy of the system is not constant  System: trampoline
Energy of the system is not constant  System: girl
Energy of the system is not constant  System: girl + trampoline
Energy of the system is constant System: girl + trampoline + Earth

________________________________________