Physical Science Work, Efficiency and Mechanical Advantage practice problems – Worksheet #3 Useful formulas: Efficiency: Wout/W in X 100 MA = weight (output force) effort (input force) MA = effort arm (length) resistance length 1. A ramp is used to load furniture onto a moving truck. The person does 1240 J of work pushing the furniture up the ramp, and the ramp does 822 J of work. Calculate the efficiency of the ramp. 2. A lever does 765 J of work and the person using the lever applies 890 J of work. What is the efficiency of the lever? 3. A mover uses a ramp to load a crate of nails onto a truck. The crate, which must be lifted 1.4 m from the street to the bed of the truck, is pushed along the length of the ramp. If the ramp is 4.6 m long and friction between the ramp and crate can be ignored, what is the mechanical advantage of the ramp? 4. A pulley is used to raise a heavy crate. With the pulley it only takes an effort force of 223 N to provide a resistance force of 1784 N. What is the mechanical advantage of this pulley? 5. Justin is riding his bike up Dunmore Hill. The effort force from his feet on his pedals is 1160N. The resulting load force to move the bike forward is 675N. What is the mechanical advantage of the bike? 6. A force of 30 N is applied to a screwdriver to pry the lid off of a can of paint. The screwdriver applies 75 N of force to the lid. What is the mechanical advantage of the screwdriver? 7. The power steering in an automobile has a mechanical advantage of roughly 75. If the input force on the steering wheel is 49 N, what is the output force that turns the car’s front wheels? 8. Susan and Jake’s truck gets stuck in the mud. They used a tree branch as a lever to lift the truck out of the mud. They applied an effort force of 700N to the branch and the back of the truck weighs 2100N. What is the mechanical advantage of the tree branch lever? 9. If the branch lever mentioned in question 2, the effort arm was 3.2m long and the resistance arm was 0.6m, then what is the mechanical advantage? 10. If Susan and Jake made the effort arm 1m instead of 3.2m then what is the mechanical advantage? Is this easier or harder to lift the load. more Physical Science 11. A wheelbarrow has a mechanical advantage of 2.2. The output distance extends from the load’s center of mass to the wheel and the input distance is from the handles to the wheel. For an output distance of 0.45 m, what is the input distance? 12. An Archimedean screw is a screw within a closely fitting cover, so that water can be raised when the screw is turned. Suppose the screw has a mechanical advantage of 12.5. If the screw is turned several times, so that the input distance is 15.7 m, how much has water been lifted upward by the screw (output distance)?
