Energy

A crane lowers a steel girder into place at a construction site. The girder moves with constant speed. Consider the work

W

g gravity and the work

W

T done by done by the tension in the cable. Which of the following is correct?

A.

B.

C.

D.

E.

W

g is positive and

W

T is positive.

W

g is negative and

W

T is negative.

W

g is positive and

W

T is negative.

W

g and

W

T are both zero.

W

g is negative and

W

T is positive.

A crane lowers a steel girder into place at a construction site. The girder moves with constant speed. Consider the work

W

g gravity and the work

W

T done by done by the tension in the cable. Which of the following is correct?

A.

E.

W

g is positive and

W

T is positive.

B.

D.

W

g is negative and

W

T is negative.

C. W g is positive and W T is negative.

W

g and

W

T are both zero.

W

g is negative and

W

T is positive.

The tension force is opposite the direction of motion while the gravitational force is in the same direction as the motion. The

cos(theta)

term in the work formula is negative.

Which force does the most work?

A. The 6 N force.

B. The 8 N force.

C. The 10 N force.

D. They all do the same amount of work.

Which force does the most work?

A. The 6 N force.

B. The 8 N force.

C. The 10 N force.

D. They all do the same amount of work.

Rank in order, from largest to smallest, the gravitational potential energies of balls 1 to 4.

A. (

U

g ) 1 > (

U

g ) 2 > (

U

g ) 3 > (

U

g ) 4 B. (

U

g ) 4 > (

U

g ) 3 > (

U

g ) 2 > (

U

g ) 1 C. (

U

g ) 1 > (

U

g ) 2 = (

U

g ) 4 > (

U

g ) 3 D. (

U

g ) 3 > (

U

g ) 2 = (

U

g ) 4 > (

U

g ) 1 E. (

U

g ) 4 = (

U

g ) 2 > (

U

g ) 3 > (

U

g ) 1

Rank in order, from largest to smallest, the gravitational potential energies of balls 1 to 4.

A. (

U

g ) 1 > (

U

g ) 2 > (

U

g ) 3 > (

U

g ) 4 B. (

U

g ) 4 > (

U

g ) 3 > (

U

g ) 2 > (

U

g ) 1 C. (

U

g ) 1 > (

U

g ) 2 = (

U

g ) 4 > (

U

g ) 3

D. (U g ) 3 > (U g ) 2 = (U g ) 4 > (U g ) 1

E. (

U

g ) 4 = (

U

g ) 2 > (

U

g ) 3 > (

U

g ) 1 Use the formula U = mgy

A small child slides down the four frictionless slides A–D. Each has the same height. Rank in order, from largest to smallest, her speeds

v

A to

v

D at the bottom.

A.

B.

C.

D.

E.

v

A =

v

B =

v

C =

v

D

v

D >

v

A =

v

B >

v

C

v

D >

v

A >

v

B >

v

C

v

C >

v

A =

v

B >

v

D

v

C >

v

B >

v

A >

v

D

A small child slides down the four frictionless slides A–D. Each has the same height. Rank in order, from largest to smallest, her speeds

v

A to

v

D at the bottom.

A. v A = v B = v C = v D

B.

v

D >

v

A =

v

B >

v

C C.

D.

v

D >

v

A >

v

B >

v

C

v

C >

v

A =

v

B >

v

D E.

v

C >

v

B >

v

A >

v

D

A spring-loaded gun shoots a plastic ball with a speed of 4 m/s. If the spring is compressed twice as far, the ball’s speed will be A. 16 m/s.

B. 8 m/s.

C. 4 m/s.

D. 2 m/s.

E. 1 m/s.

A spring-loaded gun shoots a plastic ball with a speed of 4 m/s. If the spring is compressed twice as far, the ball’s speed will be A. 16 m/s.

B. 8 m/s.

C. 4 m/s.

D. 2 m/s.

E. 1 m/s.

Four students run up the stairs in the time shown. Rank in order, from largest to smallest, their power outputs

P

a to

P

d .

A.

B.

C.

D.

E.

P

b >

P

a =

P

c >

P

d

P

d >

P

a =

P

b >

P

c

P

d >

P

b >

P

a >

P

c

P

b >

P

a >

P

c >

P

d

P

c >

P

b =

P

a >

P

d

Four students run up the stairs in the time shown. Rank in order, from largest to smallest, their power outputs

P

a to

P

d .

A. P b > P a = P c > P d

B.

P

d >

P

a =

P

b >

P

c C.

D.

E.

P

d >

P

b >

P

a >

P P

b >

P

a >

P

c >

P

d

P

c >

P

b =

P

a >

P

d c