Chapter 8 test review

If a mouse and an elephant both run with the same kinetic energy, can you say which is running faster? Explain in terms of the equation for KE.

a mouse because it's lighter

How does energy conservation apply to a pendulum?

When a pendulum swings, potential energy is transformed into kinetic energy, and then back again to potential energy as the speed and elevation of the pendulum vary during the motion.

A system using more than one simple machine is called a

compound machine

The ______ is a unit to measure power

watt

A device that helps do work is called a

machine

a machine with a _________ of two doubles the force applied to the machine

mechanical energy

work/time =

power

the _______ of a machine compares its work output with the work input

mechanical efficiency

a lever is an example of a _________

simple machine

force x distance

work

the ______is a unit used to measure work

joule

a quantity measured with respect to another measured quantity such as speed is call a ______

rate

a machine will change the _____ or _______ of the force used to do work

size or direction

due to _____, it is unrealistic to think that a machine will ever be 100% efficient

friction

How much work is done by a force of 45 N that moves an object 1.4 m?

45 x 1.4 = 63 joules

A cat weighing 70 N jumps 3 m onto a fence. How much work does the cat do?

70 x 3 = 210 joules

You do 3450 J of work to slide a box across the floor in 18 s. Calculate your power

3450/18 = 191.6 N

If it takes 23 s for you to do 450 J of work, what is your power output?

450/23 = 19.5 N

John works at a construction sight. The foreman told him that with a particular crowbar he needs 70 N of force to lift 600 N. What is the mechanical advantage of the crowbar?

600/70 = 8.6

If you needed to put 16 N of work into a machine to get 12 N of work out, what is the mechanical efficiency of the machine?

12/16= 0.75

What will be the KE of an arrow having a PE of 50 J after it is shot from a bow?

50 J

What is efficiency of a machine that requires a 100 J of input energy to do 35 J of useful work?

35%

Calculate the KE of a 5 kg toy cart that moves at 10 m/s

1/2 (5)(10) squared= 250 J

A toy cart moves with a kinetic energy of 10 J. What will its kinetic energy be if its speed is doubled?

1/2 (10)(2) squared= 40 J

Why can't a machine be 100% efficient?

friction

What's the difference between force and work?

Distance

Why do we use machines?

We use machines to make work easier to perform.