BackQuestion 1 : A machine can (1) creat energy, (2) transform energy from one form into another, (3) transfer energy from one place to another.
A) (1) only B) (3) only C) (1) and (2) D) (2) and (3) E) (1)~(2) and (3)
Question 2 : A motor specified 200 V, 1000 W is used to wind up a cable connected to a pulley system. The pulley system raises a load of 100 kg at a steady speed of 0.5 m-1. What is the overall efficiency ?
A) 5% B) 10% C) 25% D) 50% E) 100%
Question 3 : Which of the followings is/are example of the first class lever in which the fulcrum is between the load and effort? (1) beam balance, (2) see-saw, (3) scissors.
A) (1) only B) (3) only C) (1) and (2) D) (2) and (3) E) (1)~(2) and (3)
Question 4 : A screw-jack is used to raise a 2000 N load. The jack has a handle length of 0.3 m and pitch of the screw is 3 mm. If the efficiency of the screw-jack is 20 %, how much energy is wasted when the load is raised by 0.5 m ?
A) 200J B) 800J C) 1000J D) 1400J E) 5000J
Question 5 : Which of the following ways may increase the efficiency of a machine ? (1) increase the effort, (2) increase the load, (3) add lubricant to reduce friction.
A) (1) only B) (2) only C) (3) only D) (1) and (3) E) (2) and (3)
Question 6 : The efficiency of the screw-jack can be improved by (1) increasing the length of the handle, (2) decreasing the length of a pitch, (3) adding lubricating oil.
A) (3) only B) (1) and (2) C) (1) and (3) D) (2) and (3) E) (1)~(2) and (3)
Question 7 : The efficiency of a lift is 40%. If a power of 50 kW is input to the lift, what is the maximum number of passengers of average mass of 70 kg that can be raised at a speed of 2 m s-1?
A) 7 B) 10 C) 11 D) 14 E) 15
Question 8 : Statment 1: The screw jack is usually of high efficiency. BECAUSE Statment 2: The frictional loss of the screw jack is usually low.
A B C D E
Question 9 : Statment 1: To cycle up a slope, it is easier to go straight up than to take a zig-zag path. BECAUSE Statment 2: One does not hace to exert too great a force to go up.
A B C D E
Question 10 : Statment 1: In a machine the effort must be smaller than the load. BECAUSE Statment 2: A machine can save effort.
A B C D E
Answer~:D D E D E A D E D D