Introduction to Machines Answers

Lucy needs to lift a crate to a shelf 20 m high. She does 12,000 J of work on a machine to help her. The machine exerts a force of 500 N to lift the crate.What is the efficiency of the machine?

Students in Ms. Delgado’s science class built machines. They measured the input and output forces. The results of four students are listed in the table. Which lists the students in order from student whose machine has the least mechanical advantage to student whose machine has the greatest mechanical advantage?

A machine has a mechanical advantage of 4.5. What force is put out by the machine if the force applied to the machine is 800 N?

A machine has a mechanical advantage of 5. What force should be applied to the machine to make it apply 3000 N to an object?

Percy pulls on a rope that is held up by a pulley, like the one shown. The pulley is near the ceiling, and the other end of the rope is attached to a crate. Percy applies 75 N of force to the rope, and the rope lifts the crate by applying a force of 75 N.

Tas watches as his uncle changes a flat tire on a car. His uncle raises the car using a machine called a jack. Each time his uncle pushes down on the jack handle, the car rises up. Tas sketches the jack and labels it using the symbols F, to represent force, and d, to represent distance. He uses large and small letters to compare the sizes of the forces and distances.Which set of labels is correct for the side of the jack that Tas’s uncle pushes on?