unit 4

Circle the simple machines and put a box around the complex machines. [simple pulley, lever, screw, bicycle, inclined plane, wheel and axle, scissors, pulley system called a block and tackle]

square pulley bicycle scissors block and tackle circle lever screw wheel and axle incline plan

If two people do the same amount of work but one does the work faster than the other then do the two people have the same amount of power? Why or why not?

yes because they did the same work

An inclined plane reduces the force need to move and object by [increasing/decreasing] the ________________ through which the force is applied.

​Inclined planes and pulleys both lower the amount of force needed to raise a load or object. Inclined planes reduce the amount of force required by increasing the distance an object must travel. Simple pulleys change the direction of the force used to lift an object over a distance.

A person puts 50 N of force into a lever. The lever lifts a 500 N box. What is the mechanical advantage of the lever?

10

If 700 Joules of work is done in 70 seconds then what is the power?

10

What is the machine efficiency of a machine that has a work input of 200 Joules and a work output of 50 Joules?

4

What is the machine efficiency of a machine that has a work input of 150 Joules and a work output of 35 Joules?

4.2

If a 50 kg box is moved 10 m in 10 seconds then what is the power?

50

If a 80 kg ball is moved across a floor for 80 m then how much work is done?

6400

A person put 25 N of force into a wheel and axle and moves a 200 N box. What is the mechanical advantage of the wheel and axle?

8

What is the kinetic energy of an object with a mass of 80 kg and a velocity of 4.5 m/s?

810

If a box that is 70 kg is moved up 140 m then how much work is done?

98000

What two factors determine an object's gravitational potential energy?

Gravitational Potential Energy is determined by three factors: mass, gravity, and height.

At what point on a roller coaster is the gravitational potential energy the greatest?

Gravitational potential energy is greatest at the highest point of a roller coaster and least at the lowest point. Kinetic energy is energy an object has because of its motion and is equal to one-half multiplied by the mass of an object multiplied by its velocity squared (KE = 1/2 mv2).

At what point on a roller coaster is the gravitational potential energy the lowest?

Gravitational potential energy is greatest at the highest point of a roller coaster and least at the lowest point. Kinetic energy is energy an object has because of its motion and is equal to one-half multiplied by the mass of an object multiplied by its velocity squared (KE = 1/2 mv2).

Does increasing the velocity of an object increase its potential energy? Why or why not?

Increasing the speed of an object does not affect its motion energy.

What is the formula for kinetic energy?

KE=1/2mv^2

Kinetic energy is energy due to ____________________.

Kinetic energy, form of energy that an object or a particle has by reason of its motion. If work, which transfers energy, is done on an object by applying a net force, the object speeds up and thereby gains kinetic energy.

In order for work to be done on an object there has to be a force, there has to be movement of the object, and the movement and the force MUST be in the _________________ direction.

Newton's first law of motion states that there must be a cause—which is a net external force—for there to be any change in velocity, either a change in magnitude or direction. An object sliding across a table or floor slows down due to the net force of friction acting on the object.

What is the formula for mechanical advantage? Are there any units for mechanical advantage?

The mechanical advantage of a machine is the ratio of the load (the resistance overcome by a machine) to the effort (the force applied). There is no unit for mechanical advantages since the unit for both input and output forces cancel out.

Why will machine efficiency never be 100%?

The output work is always less than the input work because some of the input work is used to overcome friction. Therefore, efficiency is always less than 100 percent. The closer to 100 percent a machine's efficiency is, the better it is at reducing friction.

What is the formula for power? What is the unit for power?

The standard metric unit of power is the Watt. As is implied by the equation for power, a unit of power is equivalent to a unit of work divided by a unit of time. Thus, a Watt is equivalent to a Joule/second.

Energy and work both are measured in units of ________________.

The standard unit used to measure energy and work done in physics is the joule, which has the symbol J. In mechanics, 1 joule is the energy transferred when a force of 1 Newton is applied to an object and moves it through a distance of 1 meter. Another unit of energy you may have come across is the Calorie.

Mechanical energy is the sum of ________________ energy and ______________ energy in a system such as a roller coaster.

The total amount of mechanical energy is merely the sum of the potential energy and the kinetic energy.

The power of a machine measures what?

The unit of measurement for power is the (W). One watt is equal to one joule of work done in one second.

How can you reduce friction in a machine?

The use of bearing surfaces that are themselves sacrificial, such as low shear materials, of which lead/copper journal bearings are an example. Replace sliding friction with rolling element friction, such as with the use of rolling element bearings.

What is the formula for machine efficiency? What is machine efficiency expressed in?

The work efficiency formula is efficiency = output / input, and you can multiply the result by 100 to get work efficiency as a percentage.

What is the equation for work? What is the unit for work?

Work can be calculated with the equation: Work = Force × Distance. The SI unit for work is the joule (J), or Newton • meter (N • m). One joule equals the amount of work that is done when 1 N of force moves an object over a distance of 1 m.

A bar that is free to pivot about a fixed point is a ___________.

fulcrum

The amount by which machine multiplies an effort force is called the ______________ advantage.

mechanical advantage. The amount by which a machine multiplies an input (effort) force is called what. screw. An inclined plane wrapped around a cylindrical post is a ___ 1.