The human perception of the frequency of a sound wave is called:

Sound waves are classified as:

A system absorbs 120J of heat and does 40J of work. What is the change in internal energy?

In simple harmonic motion, where is acceleration the greatest?

What is the period of a wave with frequency f=0.5 Hzf = 0.5 \,\text{Hz}? T=1fT = \frac{1}{f}​

Which PREPOSITION must be used when a second verb in infinitive form follows the verbs EMPEZAR or COMENZAR?  Yo empiezo ____ trabajar.  Yo comienzo _____ trabajar.  BOTH OF THESE VERBS ARE STEM CHANGING VERBS.

Which words are part of the complete DIRECT OBJECT of this sentence and have to be REPLACED by the DIRECT OBJECT PRONOUN?  Yo estudio las grandes civilizaciones mesoamericanas.

The verb ESTAR is used in sentences that also use prepositions in order to state or describe the position of nouns in the context of what is happening in the sentence.  Which preposition would best work with this sentence using the verb ESTAR?  Rodrigo y Mariela _____ _______ del hotel esperando un taxi.  HINT:  Also check that the subject and verb form of ESTAR agree.  Then check that the preposition makes sense with what is happening in the sentence.

Which sentence using SER is incorrect?

Stem changing verbs deviate from the regular patterns of conjugation of regular verbs. When a stem changing verb is conjugated, it has a vowel change in the last syllable of the stem. These changes are communicated by using notation like (e:ie) or (o : ue). Look at the following four verbs and pick the one that is an example of a stem changing verb.