A 3.0-kg block moves up a 40° incline with constant speed under the action of a 26-N force acting up and parallel to the incline. What magnitude force must act up and parallel to the incline for the block to move down the incline at constant velocity?
a. 14 N
b. 12 N
c. 16 N
d. 18 N
e. 25 N
B
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According to our modern science, which of the following best explains why the vast majority of the mass of our solar system consists of hydrogen and helium gas?
A) Hydrogen and helium are the most common elements throughout the universe, because they were the only elements present when the universe was young. B) Hydrogen and helium are produced in stars by nuclear fusion. C) All the other elements escaped from the solar nebula before the Sun and planets formed. D) All the other elements were swept out of the solar system by the solar wind.
Bats can detect small objects such as insects that are of a size on the order of a wavelength. If bats emit a chirp at a frequency of 60 kHz and the speed of soundwaves in air is 330 m/s, what is the smallest size insect they can detect?
A. 1.5 mm B. 3.5 mm C. 5.5 mm D. 7.5 mm E. 9.8 mm
A thin converging lens is found to form an image of a distant building 24 cm from the lens. If an object is placed 16 cm from the lens, how far from the object will the image be?
A) 64 cm B) 72 cm C) 32 cm D) 96 cm E) 48 cm
A concave mirror has a focal length of 20 cm. What is the magnification if the object's distance is 100 cm?
a. 1/2 b. 1/4 c. ?2 d. 4 e. ?1/4