Waves on a lake pass under a floating bird causing the bird to bob up and down with a period of 2.5 seconds. If the distance from wave trough to wave trough is 3.0 meters, what is the speed of the wave?
A) 0.21 m/s
B) 1.2 m/s
C) 1.9 m/s
D) 2.1 m/s
E) 1.5 m/s
B
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Sophia accelerates in her car from 0 to 72km/hour in 8.0 seconds. What’s her acceleration?
a. a = 2.5 m/s2
b. a = 3.5 m/s2
c. a = 4.5 m/s2
d. a = 6.5 m/s2
You and a classmate are discussing how much work one must do to lift a box of mass m a vertical distance h. Your classmate argues, “You have to exert an upward force on the box at least equal in magnitude to the box’s weight 
, and you lift the box upward a distance h, so you must do work equal to 
. But in addition,” your classmate continues, “ you must increase the box’s gravitational potential energy by 
to lift the box.” What amount of work do you think you need to do on the box to lift it a height h? Be prepared to defend your response. (Hint: What is the system here?)
A. Zero work
B. About 
(if you move the box slowly)
C. Significantly greater than 
but less than 
D. About 
(if you move the box slowly)
E. Significantly greater than 
A pencil has
A. no nuclei in it. B. no electric charges in it. C. enough positive charge in the nuclei to balance the negative charge of the electrons. D. electrons that are not attracted to nuclei.
A balloon of negligible mass is filled with 300 m3 of helium. How big a payload can the balloon lift? (The density of air is 1.29 kg/m3; the density of helium is 0.18 kg/m3.)
a. 150 kg c. 333 kg b. 300 kg d. 444 kg