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25 questions from the mechanical aptitude practice test.
10 questions, graded as you go, with the reason for every answer. No sign-up.
Which of these tools works as a third-class lever, with the effort applied between the fulcrum and the load?
B. A pair of tweezers
In tweezers the joined end is the fulcrum, the fingers squeeze in the middle and the load is at the tips. A bottle opener puts the load (the cap) between the fulcrum and the hand, which makes it second class.
Reference: Simple machines: the three classes of lever
A first-class lever has a 200 lb load 2 ft from the fulcrum. The effort is applied 8 ft from the fulcrum on the other side. Ignoring the weight of the lever, what effort balances the load?
Answer in lb.
50 lb
Effort × 8 ft = 200 lb × 2 ft = 400 lb-ft. Effort = 400 ÷ 8 = 50 lb.
Reference: Simple machines: law of the lever (effort × effort arm = load × load arm)
A nutcracker is hinged at one end. A nut sits 1 in from the hinge and the hand squeezes the handles 6 in from the hinge with 15 lb. What force is applied to the nut?
Answer in lb.
90 lb
Moments about the hinge: force on nut × 1 in = 15 lb × 6 in = 90 lb-in. Force on nut = 90 lb.
Reference: Simple machines: law of the lever (effort × effort arm = load × load arm)