Will someone please help me with these physics questions.

Question

Now assume that all of the potential energy went into kinetic right as it is about to hit the bottom. What would be the value for the kinetic energy? 

a. less

b. same

c. more

d. not information

 

At which point(s) does the water undergo a phase change? (Choose all that apply)

C

D

B

A

When a substance's temperature increases,

a. the volume of the substance decreases.

b. energy is removed from the system.

c. kinetic energy is added to the particles of the substance.

d. the number of molecules in the substance changes.

An engine absorbs 2234 J as heat from a heat reservoir and gives off 789 J as heat to a cold reservoir during each cycle. What is the efficiency of the engine?

a. 65%

b. 34%

c. 83%

d. 53%

Answer 1

All the potential energy is converted into kinetic energy when dropping something from a height (neglecting air resistance and energy lost as heat or sound), therefore the kinetic energy will steadily increase until it reaches the ground, therefore C for #1.

Water undergoes phase changes when the temperature is constant (no slope), therefore points B and D for #2.

Temperature is proportional to kinetic energy of molecules, therefore if temperature goes up so does the kinetic energy of the molecules, therefore C for #3.

The efficiency of an engine is the ratio of output energy / input energy. The output energy is 789 J and the input energy is 2234 J, therefore the efficiency is 789/2234 x 100% = 35%, so B for #4.