John's face is 20 cm in front of a concave shaving mirror. If he observes his image to be twice as big and erect, what is the focal length of the mirror?
A)
10 cm
B)
20 cm
C)
30 cm
D)
40 cm
E)
50 cm
D
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Momentum: Two satellites with equal masses are traveling toward each other in deep space. One is traveling at 0.550c and the other at 0.750c. The satellites collide and somehow manage to stick together. What is the speed of the combined object after the collision?
A. 0.100c B. 0.113c C. 0.150c D. 0.175c E. 0.311c
An organ pipe is open at both ends. The frequency of the fourth mode is 316 Hz higher than the frequency of the third mode. If the speed of sound is 340 m/s, then what is the length of the organ pipe?
A. 53.8 cm B. 59.8 cm C. 60.3 cm D. 62.8 cm E. 64.7 cm
A hydraulic press multiplies a force by 100, which is compensated by
A) energy, which is divided by 100. B) the lesser distance through which the force acts. C) the time through which the force acts. D) the mechanism providing the force. E) none of the above
A person's eye lens is 2.8 cm from the retina, and his near point is at 25 cm. What must be the focal length of his eye lens so that an object at the far point of the eye will focus on the retina?
A) -2.8 cm B) 2.8 cm C) -2.4 cm D) 2.4 cm E) 2.2 cm