Work and Energy

Question 1

Kinetic energy=? Units=?

Answer 1

K=1/2mv^2

units=J=Newton x meter

Question 2

Gravitational PE=? Units=?

Answer 2

U=mgh

units=J=Newton x meter

Question 3

Elastic PE=? units=?

Answer 3

U=1/2kx^2 (k=spring constant, x=amt of compression or stretch)

units=J=Newton x meter

Question 4

Total mechanical energy=? units=?

Answer 4

E=U+K

units=J=Newton x meter

Question 5

Conservation of mechanical energy=?

Answer 5

change in E=change in U+ change in K=0

Question 6

Work(nonconservative)=? units=?

Answer 6

W=change in E=change in U+ change in K=0

units=J=Newton x meter

Question 7

Mechanical work=? units=?

Answer 7

W=Fdcos(theta)

units=J=Newton x meter

Question 8

Piston work=? units=?

Answer 8

W=P x deltaV

units=J=Newton x meter

Question 9

Power=? units=?

Answer 9

P= Work/time = change in energy/time

Units=Watt=J/s

Question 10

Net work=? units=?

Answer 10

W(net)=change in kinetic energy=Kf-Ki

units=J=Newton x meter

Question 11

Mechanical advantage=? units=?

Answer 11

F (out)/ F (in)

unit-less! (it is a ratio)

Question 12

Efficiency=?

Answer 12

W (out)/ W(in) = (load x load distance)/(effort x effort distance)`

Question 13

What does the spring constant depend on?

Answer 13

the stiffness of the spring

Question 14

When does a spring have elastic potential energy?

Answer 14

When it is stretched or compressed from its equilibrium length (the length at which it is completely relaxed.)

Question 15

What is work? units?

Answer 15

the amount of energy transferred from one system to another.

units=J=Newton x meter

Question 16

What is power?

Answer 16

Rate at which energy is transferred from one system to another.

Question 17

What are conservative forces?

Answer 17

Path independent, do not dissipate mechanical energy of a system.

Conserve mechanical energy.

EX: gravity, electrostatic forces, elastic (nearly)

Question 18

What are non-conservative forces?

Answer 18

Path dependent.

Cause dissipation of mechanical energy (as heat or chemical energy.)

EX: friction, air resistance, viscous drag.

Question 19

What is mechanical advantage?

What is increased by a simple system? what is decreased?

Answer 19

The factor by which simple systems increase the ability to do work.

Force required - decreased.

Distance through which force is applied - increased.

Machines: plane, wedge, wheel and axle, lever, pulley, screw.

Question 20

What is efficiency?

Answer 20

ratio of a simple machine’s work output to work input when nonconservative forces are taken into account.

Question 21

What is electrical potential energy?

Answer 21

The amount of energy needed to bring a charge from infinitely far away to a given position close to a source charge.

Question 22

Electrostatic force

Answer 22

F= kq1q2/r^2

Question 23

Electrostatic potential energy

Answer 23

U=Fxr

U= kq1q2/r

Question 24

Electrostatic potential

Answer 24

V=U/q

V= kq1/r

Question 25

Electric field

Answer 25

V=Ed (capacitor)

E=kq1/r2