Question

8. How can you make the work output of a machine greater
than the work input?
a. by decreasing friction
b. by increasing the input force
c. by increasing the output distance
d. none of the above
9. If you know the input distance and output distance of a
machine, which of the following can you calculate?
a. work b. actual mechanical advantage
c. efficiency d. ideal mechanical advantage
10. A 100-m long ski lift carries skiers from a station at the foot
of a slope to a second station 40 m above. What is the IMA
of the lift?
a. 0.4 b. 2.5
c. 40 d. 140
11. The efficiency of a machine is always less than 100 percent
because
a. a machine cannot have an IMA greater than 1.
b. some work input is lost to friction.
c. the work input is too small.
d. the work output is too great.
12. A motor with an efficiency rating of 80 percent must supply
300 J of useful work. What amount of work must be
supplied to the motor?
a. 80 J b. 240 J
c. 375 J d. 540 J
13. Which of the following is an example of a wheel and axle?
a. a doorknob b. an automobile steering wheel
c. a jar lid d. a pencil
14. A machine is classified as a compound machine if it
a. has moving parts.
b. has an IMA greater than 1.
c. is made up of two or more simple machines that operate
together.
d. is very effici

Answer 1

8. d — none of the above. Work output cannot exceed work input (energy conservation); reducing friction only reduces losses but can't make output > input.

9. d — ideal mechanical advantage. IMA = input distance / output distance.

10. b — 2.5. IMA = 100 m / 40 m = 2.5.

11. b — some work input is lost to friction (and other losses), so efficiency < 100%.

12. c — 375 J. Input = useful output / efficiency = 300 J / 0.80 = 375 J.

13. a — a doorknob. (A steering wheel is also a wheel-and-axle, but the typical single-best example given is a doorknob.)

14. c — made up of two or more simple machines that operate together.