Planning on taking the ASVAB Mechanical Comprehension Technical Subtest? Try out a few practice questions!
D: Although the mass and time are unknown, they are not needed to solve the problem. When the ball is 5 m above the ground all its energy is PE, but when it hits the ground all its energy is KE. Since energy is conserved, set PE = KE or mgh = (1/2)v^2. The mass cancels out and, since the question asks for the approximate speed, g = 10 will suffice. 2 × 10 × 5 = v^2 and 100 = v^2, so v = 10.
B: Since the pressure is the same throughout a closed hydraulic system and force is equal to pressure times the area over which it is applied, F1 must be greater than F2. Also, the work (force times distance) must be equal on both sides. Since F1 > F2, it follows that d2 > d1.
C: Tools do use the principles of mechanics but measuring devices do not. Similarly, machines that transmit or use energy are governed by these principles, but the study of mechanics is not limited to machines. While trajectories are a type of motion, the more broad category of “motion” is the proper answer.
D: The first step is to convert the mass given into a force, which will be its weight. The force of the weight is mg = 100 kg x 10 m/s^2 = 1,000 N. Since there are 4 pulleys, the mechanical advantage is 4:1, meaning that 1/4 of the force can be applied over 4 times the distance to pull up the mass. Since the weight is 1,000 N, the force applied would be 250 N.
D: Kinetic friction is exhibited when surfaces/objects move past one another. The normal force, which is a factor of the weight of the object, will affect friction (for example: move your hand across a table lightly and then again with more force; increased force leads to increased friction). The nature and area of the surfaces in contact with each other will also affect the friction that develops between two surfaces (for example: moving your hand across a desk with oil on it is a lot easier than with honey; also, moving one finger across a desk develops less friction than moving your entire hand). The speed at which the surfaces move past each other, however, does not impact the frictional forces (though more heat may be generated).