Concept 2 Conservation of Energy

Potential energy is defined as

• Energy stored in the object

• Energy of motion

• Energy stored in the bonds of molecules

• Heat energy

Tags

NGSS.MS-PS3-2

A 4 kg block is pushed up an incline that makes a 30⁰ angle with the horizontal, as shown in the figure. Once the block is pushed a distance of d=5.0  m up the incline, the block remains at rest. What is the approximate change in the gravitational potential energy of the block-Earth system when the block is held at rest compared to its original location at the bottom of the incline?

• 0 J

• 100 J

• 100 square root of 3

• 200J

Tags

NGSS.HS-PS2-4

NGSS.HS-PS3-1

NGSS.HS-PS3-2

The unit for energy and work is

• J

• N

• m/s

• m/s/s

An object of mass M is attached to a string of negligible mass and spun in a vertical circle of radius R, as shown in the figure above. As the object’s height increases, its speed decreases such that the object-Earth system’s total mechanical energy remains constant. By how much does the object’s kinetic energy decrease in moving from point O, the lowest point on the circle, to point P, the highest point on the circle?

• 
• 
• 
• 

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-2

The law of conservation states that

• every action has an equal and opposite reaction
• all matter has thermal energy
• energy cannot be created or destroyed, only changes form
• heat moves from an object of higher temperature to an object of lower temperature

Tags

NGSS.HS-PS3-1

The ability to do work is called

• energy
• thermal
• kinetic
• potential

Tags

NGSS.HS-PS3-3

The surface of an incline is coated with an experimental substance that is intended to reduce the frictional force between a block and the surface of the incline. A 2 kg

block is placed at the top of the incline at a height of 1.8 m

, as shown in the figure. After the block is released from rest, the block slides down the incline and a motion detector at the bottom of the incline measures the block’s speed as 5.8m/s after the block is no longer on the incline. Which of the following claims is correct about the experimental substance?

• The experimental substance reduced all the frictional force because all the gravitational potential energy of the Earth-block system at the top of the incline was converted into the kinetic energy of the block at the bottom of the incline.

• The experimental substance did not reduce all the frictional force because some of the gravitational potential energy of the Earth-block system at the top of the incline was converted into nonmechanical energy.

• The effectiveness of the experimental substance cannot be determined because the speed of the block at the bottom of the inline, as measured by the motion detector, indicates that the block has more energy at this location than the Earth-block system had at the top of the incline.The effectiveness of the experimental substance cannot be determined because the speed of the block at the bottom of the inline, as measured by the motion detector, indicates that the block has more energy at this location than the Earth-block system had at the top of the incline.

• The effectiveness of the experimental substance cannot be determined without knowing the magnitude of the frictional force between the block and the incline before and after the experimental substance was applied to the incline.

Tags

NGSS.HS-PS2-1

A student is conducting an experiment to analyze the mechanical energy of a block-spring system. The student places a block of mass 2kg on a horizontal surface and attaches the block to a horizontal spring of negligible mass and spring constant 100N/m, as shown in the figure. There is negligible friction between the block and the horizontal surface. The other end of the spring is attached to a wall. The block-spring system is initially at the spring’s equilibrium position.

The student wants to collect data of the block-spring system that can be used to determine the work done on the spring by the block when the spring is compressed. Which of the following includes only the measuring devices that the student will need in order to collect the data?

• Force probe and meterstick

• Stopwatch and meterstick

• Stopwatch and force probe

• Force probe, stopwatch, and meterstick

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-2

A pendulum is released from point C.  Which statement is correct as it  swings from C to A?

• The PE increases and KE decreases
• The KE increases and PE decreases.
• The PE is maximum at A.
• The KE is maximum at C and B.

Which of the following is an example of a transformation of potential energy to kinetic energy?

• a truck slowing down
• a car climbing up a hill
• an airplane traveling at constant speed
• falling object