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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Four identical particles (mass of each = 0.40 kg) are placed at the vertices of a rectangle (2.0 m × 3.0 m) and held in those positions by four light rods which form the sides of the rectangle. What is the moment of inertia of this rigid body about an axis that passes through the mid-points of the longer sides and is parallel to the shorter sides?
a. 2.7 kg×m2 b. 3.6 kg×m2 c. 3.1 kg×m2 d. 4.1 kg×m2 e. 1.6 kg×m2
The rotational inertia of an object depends on
A. how its mass is distributed about the spin axis. B. how fast it is spinning. C. its color. D. the amount of torque applied to it. E. None of these choices are correct
A rocket with an initial mass of 1000 kg adjusts its thrust by varying the rate at which mass is ejected. The ejection speed relative to the rocket is 40 km/s. If the acceleration of the rocket is to have a magnitude of 20 m/s2 at an instant when its mass is 80% of the original mass, at what rate is mass being ejected at that instant? Ignore any external forces on the rocket.
A. 0.40 kg/s B. 0.50 kg/s C. 0.60 kg/s D. 0.70 kg/s E. 0.80 kg/s
The largest volumes of magma extruded on the continents are
A) flood and plateau basalts. B) central-vent type volcanoes. C) batholiths. D) from volcanoes with a high silica content.