When a boulder and a pebble are dropped, why does the pebble pick up speed as quickly as the boulder, even though less gravity acts on it? In other words, why do both accelerate equally?
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Answer: Acceleration depends not only on the force of gravity, but also on the mass. If the boulder is fifty times heavier than the pebble, it also has fifty times as much mass. So in accord with Newton's second law, fifty times as much force on fifty times as much mass gives the same acceleration as one-fiftieth the force on one-fiftieth the mass on the pebble. Both boulder and pebble accelerate equally. If air resistance affects motion, then the accelerations will not be equal.
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A square conducting loop is situated such that it is vertical, in the x-z plane. The earth’s gravitational field points downward (in the –z direction). The loop is dropped, and maintains its orientation in the x-z plane. A magnetic field pointing in the +y direction exists and is uniform with respect to time, but varies as a function of z: B(z)=Bo (10m-z). The loop is dropped and allowed to fall under the influence of gravitation. You observe the loop from the +y direction. Which of the following occurs?
A. The situation is unclear because we do not know the initial conditions. B. There is a clockwise induced current. C. There is a counter-clockwise induced current. D. There is no induced current.
An aluminum light pole weighs 4300 N and supports an arm of weight 700 N, with the arm center of gravity at 1.2 m left of the centroidal axis of the pole. A wind force of 1500 N acts to the right at 7.5 m above the base. The pole cross section at the base has an outside diameter of 235 mm and thickness of 20 mm. The maximum compressive stress at the base is approximately:
(A) 16 MPa
(B) 18 MPa
(C) 21 MPa
(D) 24 MPa
If the Moon is relatively far from Earth, so that the umbra does not reach Earth, someone directly behind the umbra will see
A) a penumbral lunar eclipse. B) a partial lunar eclipse. C) a partial solar eclipse. D) an annular eclipse. E) no eclipse.
Why does ion propulsion, which expels material much faster than ordinary chemical rockets, hold such promise for future space travel?
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