Free Fall: A 10-kg rock and 20-kg rock are dropped from the same height and experience no significant air resistance. If it takes the 20-kg rock a time T to reach the ground, what time will it take the 10-kg rock to reach the ground?
A. 4T
B. 2T
C. T
D. T/2
E. T/4
Answer: C
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Velma, inside a train moving at 20 m/s, throws a rock in the forward direction at 5 m/s. According to her the rock moves at 5 m/s. According to Mort, standing on Earth outside the train, the rock moves at [approximately] 25 m/s. Who is correct?
A) The Wizard of Oz. B) Velma, because she threw the rock. C) Mort, because he is standing on Earth. D) Both, relative to their own reference frames. E) Neither, because there is no universal "best" reference frame.
Vector V1 is (5i + 7j - 3k) and V2 = (7i + 2 j + 14k). The scalar product of these two vectors is:
(A) 7.0 (B) -5.8 (C) 2.5 (D) 3.4
A block is dragged at constant velocity across a level surface by a force of 6 N. What is the force of friction between the block and the surface?
A) less than 6 N B) more than 6 N C) 6 N D) not enough information
If one half-life for an isotope is 25,000 years, then 10 half-lives would be _______ years
a. 2,500 b. 25,000 c. 125,000 d. 250,000