Which best describes when a sonic boom occurs?

a. when a object travels at or above the speed of sound
b. when an object travels at the speed of sound
c. when an object travels below the speed of sound
d. when an object travels above the speed of sound

Unlike the idealized voltmeter, a real voltmeter has a resistance that is not infinitely large. a voltmeter with resistance rv is connected across the terminals of a battery of emf e and internal resistance r. find the potential difference vmeter measured by the voltmeter. what is vmeter?