Chapter 7 Work and Kinetic Energy7-1 Work done by a Constant Force A. Force along Displacement W = Fd Units: Nm = Joule

P7.5 (p.200)

Chapter 7 Work and Kinetic Energy7-1 Work done by a Constant Force B. Force at Angle to Displacement W = Fdcos P7.11 (p.200)

Similar to assigned 7.14

d

F

A.

B.

C.

CT1

The force acting on an object is proportional to the final speed.

Incorrect Explanation: A decrease in the rate of speeding up is due to the force being 'used up.'

A.

B.

C.

CT2

For objects falling vertically, regardless of mass, the same force applied for the same amount of time produces the same motion.

For objects on frictionless surfaces, regardless of mass, the same force applied for the same amount of time produces the same motion.

The student explains linear acceleration with a reversed or otherwise incorrect relationship between force, mass, and acceleration.

A.

B.

C.

D.

CT3

The student explains curved motion by having an outward force balancing an inward force.

The student thinks that an outward force exists with all curved motion.

A.

B.

C.

D.

CT4

A.

B.

C.

D.

The student thinks that only forces exactly in the direction of motion (or opposite) can speed up or slow down an object. All other forces just change the direction of motion.

The student thinks that all unbalanced forces on an object will either cause the object to speed up or slow down.

Chapter 7 Work and Kinetic Energy7-1 Work done by a Constant Force C. Zero, Negative and Total Work

W is zero if = 90 or 270 W is negative if 90 < < 270 WTOT = (FTOTcos)d or WTOT = W

P7.9 (p.200)

d

FTOT

Concept Question 5P7.9: The coefficient of kinetic friction k is

A. equal to fk/mg.

B. greater than fk/mg.

C. less than fk/mg.

Chapter 7 Work and Kinetic Energy7-2 Kinetic Energy (K) and the Work-Kinetic Energy Theorem K = mv2/2 WTOT = K P7.18 (p.200)

Concept Question 6P7.18b: The work of the air resistance is

A. positive

B. negative

C. zero

P7.19 (p.200)

7-3 Work Done by a Variable ForceGraphical Representation of the Work Done

by a Constant Force

F

x

Work Done by a Non-Constant Force

W = W1 + W2 = Total Area Under the Force-Displacement Curve

Work Done by a Continuously Varying Force

Work Done by a Continuously Varying Force

W = Total Area Under the Force-Displacement Curve

P7.29 (p.201)You do

7.287.32 HintW = K

W1

W2W3

0.4 0.9

7.31 (p.201)

W = ½ base x height

W = ½kx2

Concept Question 7P7.31b: The additional work to compress the spring another 0.14 meters is

A. 160J.

B. more than 160J.

C. less than 160J.

Chapter 7 Work and Kinetic Energy7-4 Power PAV = W/t Units: J/s = Watt PAV = Fv (for constant v along displacement) P7.50 (p.202)