Chapter 9 test

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A 44 kg cheetah runs at a constant speed of 31 m/s. What is its KE?

21142 J

A 65kg person climbs a ladder straight up 35m high. What is the persons GPE at the top of the ladder? Use g = 9.8 m/s^2

22295 J

From the previous question (How much work was done to push a 10 N book 5 meters?) How much power was used if it took 2 s?

25 W

What is the Effort Force by a 6-m lever with fulcrum 2m from object on a 240 N Fr?

80

Gravity=

9.8 m/s² can be rounded to 10m/s²

Work (W)

Energy used to move an object with a given displacement

Watts can also be written as

Joule / sec

Gravitational potential energy units

Joules (J)

Unit for Work

Joules (J)

Units for Kinetic Energy

Joules (J)

Kinetic Energy symbol

KE

Equation for conservation of Energy

KE + PE = Constant 1/2 × m × v² + g × m × h = Constant

Equation for Kinetic energy

KE = ½ × mass × (velocity)² ½ × m × (v)²

This shows the transformation of energy when a skate boarder goes down a ramp.

KE → GPE

This shows the transformation of energy when a skate boarder goes up a ramp

KE → GPE

Net Force (Fnet)

The sum of all forces acting on an object (N)

Mechanical Energy

The sum of potential and kinetic energies

Compound machine

Two or more simple machines (Bicycle)

A bird flying horizontally at 550m high and has 2802 J of GPE. What is its mass?

0.52 kg

From the previous question (Two people each applied 100N of force to move a crate 3m. Whats the work done?) How much power would be used if it took them 60s?

10 W

What is the effort force of a 16 cm diameter wheel and 4 cm radius axle on a 200 N Fr?

100

A mechanical jack does 5350 J of work to lift a car 0.50m in 50s. What is the power output by the jack?

107 W

Work symbol

W

An apple with a weight of 1 N falls 1 m straight down. How much work is done by he gravitational force?

W = 1 Joule

A crane uses an average force of 5200 N to lift an I-beam 25 m, straight up. What is the work done by the crane?

W = 130,000 Joules

The brakes on a bicycle apply 125 N of frictional force to the wheels as the bike travels 14.0 m to come to a stop. How much work is done by the brakes on the wheels?

W = 1750 Joules

This equation triangle is used to calculate Work given Force and Distance

W = F *s

Average power equation triangle

W on top and P on left and t on right

Units for Power

Watts (W)

KE = 0 when this is true

When v = 0

Kinetic Energy equation for velocity

v = √2KE/m

KE = PE for a falling object when this is true

when h is at h/2

A girl with a weight of 560 N walks up some stairs that go up vertically 5.5m a. Calculate her power output if she climbs the stairs in 12.6 sec. b. Calculate her power output if she clim the stairs in 10.5 sec.

a. 244.4 W b. 293.3 W

Units for displacement

m

height units

m

Kinetic energy equation for mass

m = 2KE/ v²

Gravitational Potential energy equation for mass

m = PE ÷ (g × h)

velocity units

m/s

time symbol

t

A rower uses 120 W to do 3600 J of work on the oars. How long does it take him?

t = 30 s

Fe is the

"Effort force" (input force)

Fr is the

"Resistive Force" (Output force)

At ground what does potential energy equal?

0

Two people each applied 100N of force to move a crate 2m. Friction is 50N. What is the Fnet?

150 N

A 1200 kg car going at 18m/s. Find its KE.

194400J

A 2kg box on a shelf has 49J of GPE. How high off the ground is it?

2.5 m

From the previous question (Two people each applied 100N of force to move a crate 2m. Friction is 50N. What is the Fnet?) what is the work done on the crate?

300J

What is the mechanical advantage of an inclined plane 16m long and 4m high?

4

A 1200- kg car at the top of a 42 m hill. Calculate GPE

493920 J

A ball rolls down a frictionless half-pipe from a 4m height. How high does it go on the other side?

4m

How much work was done to push a 10 N book 5 meters?

50 J

From the previous question (Two people each applied 100N of force to move a crate 2m. Friction is 50N. What is the Fnet?) (what is the work done on the crate?)) what power was used if it took them 60s?

5W

A rower does 3600 J of work on the oars in 60.0 s. What is his power output?

60 W

Using a pulley system a crew does 2,000 J of work to lift a box that required 1200 J of work. What is the efficiency of the pulley system?

60%

Two people each applied 100N of force to move a crate 3m. Whats the work done?

600 J

A 2kg box falls off a shelf and hits the ground with 49J of KE. How fast was it going?

7 m/s

A bowling ball travels horizontally at 2 m/s and has 16J of KE. What is its mass?

8 kg

Efficiency

A ratio of output work/input work Fout/Fin

Equation for Average Power

Average Power = Work / Time P = W / t

This means to preserve or keep constant

Conservation

A ball rolls down a frictionless half pipe from a 2m height, and goes 2m on the other side due to

Conservation of Energy

Equation for simple machines

Depends on which machine

Simple machines

Does work by motion in 1 direction or axis

Input Force

Effort force applied to machine (N) Fe

Kinetic Energy (KE)

Energy of an object due to mass and velocity

Gravitational (GPE)

Energy stored by position usually height+mass+gravity

Net force symbol

Fnet

Energy Transformations

For mechanical energy KE↔PE

Equation triangle to calculate effort force of simple machines.

Fr on top Fe on left and MA on right

This is the force that opposes motion

Friction

Gravitational Potential Energy symbol

GPE

What are the two types of mechanical energy

GPE, KE

Gravitational Potential Energy equation

GPE= m × g × h mass × gravity × height

Examples of Potential Energy

Gravitational (due to "g"), Elastic (Springs, rubber bands)

Displacement (s)

Has distance and direction, object is moved by Fnet (m)

Mechanical advantage (MA)

How much machine multiplies effort force (Fin)

This is multiplied times your effort force by a simple machine

MA

MA equation for screw

MA = 2πR/ P

MA equation for incline plane

MA = L / h

MA equation for wedge

MA = L / t

MA equation for pulley

MA = N

MA equation for wheel and axle

MA = R / r

MA equation for Lever

MA= Le / Lr

This is the sum of KE + PE

ME

Net force units

N

Joules can also be written as

N × m

Conservation of Energy

Neither created nor destroyed, only transforms

Do you do work holding a bag of groceries? If so, on what axis?

No work because there is no displacement

Do you do work carrying a suitcase 5m in a straight line?

No work done because there is not force applied.

Is a scissor a simple machine?

No, it is a compound machine. It contains a wedge and a lever.

Do you do work applying a 100-N force to a car but, its not moving? Why?

No, there is no displacement

Do you do work balancing a book on your head? Why?

No, there is no displacement

Do you do work carrying a 2 N book bag 5m across the floor? Why?

No, there is no force on the bag

Average Power symbol

P

Potential energy symbol

PE

(A 2 kg ball sits on top of a 10m pole. What is PE and KE) The ball falls off the pole what is PE and KE at 5 m?) What is PE and KE just as the ball hits the ground?

PE: 0J, KE: 200J

(A 2 kg ball sits on top of a 10m pole. What is PE and KE) The ball falls off the pole what is PE and KE at 5 m?

PE: 100J, KE: 100 J

A 2 kg ball sits on top of a 10m pole. What is PE and KE?

PE: 200 J, KE: 0j

This is the name of the rate at which work is done.

Power

Average Power (P)

Rate at which work is done over a time period.

Output force

Resulting force generated by machine (N) Fe

This is a compound machine using a wedge and a lever

Scissors

Potential energy (PE)

Stored in an object by position

Energy

The amount and ability to do work in Joules (J)

This is accomplished by adding a net force to an object to move it a certain distance.

Work

Equation for Work

Work = Force × Displacement W= F × s

An object moving in the direction of Fnet has ____________________

Work down on it

Do you do work opening a car door? On what axis?

Yes, on X axis

Do you do work pushing a 200N sled 5-m across the ground? Why?

Yes, on the X axis

Do you do work pushing a door open? If so, on what axis?

Yes, on the X axis

Do you do work climbing up a 5-m ladder? Why?

Yes, on the Y axis

Do you do work typing on a keyboard? If so, on what axis?

Yes, on the Y axis

Do you do work walking up a flight of stairs? If so, on what axis?

Yes, on the Y axis

Do you do work lifting up a book bag? If so, on what axis?

Yes, on the Y axis.

What are the 6 different simple machines?

lever, wedge, inclined plane, screw, wheel and axle, pulley.

Gravitational Potential energy equation for height

h = PE ÷ (m × g)

mass units

kg

Displacement symbol

s

A crane uses an average force of 5200 N to lift and does 130,000 J to lift an I-beam, straight up. How far does the crane lift the beam?

s = 25m

time unit

seconds


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