Activity 1.1.2 Simple Machines Practice Problems

We got to take a look at a few different real life problems using simple machines.

Simple Machines: Lever

EX 1:
       A first class lever, in static equilibrium, has a 50 lb resistance forces and 15 lb effort force. The lever's effort force is located 4 ft from the fulcrum.

1. Sketch and annotate lever system described above

2. Calculate:

Actual Mechanical Advantage (AMA)
AMA= Force Resistance/Force Effort
AMA= 50 lbs/15 lbs
AMA= 3.33

3. Static Equilibrium Calculations:

 DR= Distance of Resistance Force
 M= moment (Force x distance)
 Moment Effort + Moment Resistance
-->

∑

-->M_Fulcrum= 0

(15 lbs)(4 ft) + (50 lbs)(DR)= 0

50 lbs(DR) = 60 lbs/ft

DR= 1.2 ft

EX 2:
       A wheel barrow is used to lift a 200 lb load. The length from the wheel axle to the center of the load is 2 ft. The length from the wheel and axle to the effort is 5 ft.

1. Illustrate and annotate lever system described above

2. Calculate: 

Ideal Mechanical Advantage (IMA)
IMA= Distance(effort force)/Distance(resistant force)
IMA= 5 feet/ 2 feet
IMA= 2.5
3. Static Equilibrium Calculations:

FE= Force of Effort Force
M= moment (Force x distance)
 Moment Effort + Moment Resistance

∑ M_Fulcrum= 0

(200lbs)(2ft) + (5ft)(FE)= 0

5ft (FE) = 400 lbs/ft

FE= 80 lbs

EX 3:

       A medical technician uses a pair of 4 inch long tweezers to remove a wood sliver from a patient. The technician is applying 1 lb of squeezing force to the tweezers. If more than 1/5 lb of force is applied to the sliver, it will break and become difficult to remove.

1. Sketch and annotate lever system described above

2.  Calculate:

Actual Mechanical Advantage (AMA)
AMA= Force Resistance/Force Effort
AMA= 1 lb/ (1/5) lb
AMA= 0.2

3. Static Equilibrium Calculations:

DR= Distance of Effort Force
 M= moment (Force x distance)
 Moment Effort + Moment Resistance

∑ M_Fulcrum= 0

(4 in)(1/5 lb) + (1 lb)(DE)= 0

1 lb(DE) = (4/5) lb/in

DE= 0.8 in

Simple Machines: Pulley 

EX 1:

       A construction crew lifts approximately 560 lb of material several times during a day from a flatbed truck to a 32 ft rooftop. A block and tackle system with 50 lb of effort force is designed to lift the materials.

1. Calculate: 

Actual Mechanical Advantage (AMA)
AMA= Force Resistance/Force Effort
AMA= 560 lb/50 lb
AMA= 11.2

2. How many supporting strands will be needed in the pulley system?

2 x(# of moveable pulleys) + 1(if changing direction)= # of strands

(2 x 4) +1= 9 strands