Physics Problems: Potential Energy, Force, and Work, Study notes of Physics

Download Physics Problems: Potential Energy, Force, and Work and more Study notes Physics in PDF only on Docsity!

If we know the force as a function of

position, we can calculate the

potential energy.

In 1Dimension, this is

 U

AB

=−W

AB

x=A x=B

F xd x

If we know the PE as a function of

position, we can calculate the force.

In 1Dimension, this is

In 3Dimensions, this is

F

x

dU

dx

F=−∇ U

 K U=W

NC

K

f

U

f

=K

i

U

i

If working only with conservative

forces

K

f

U

f

=K

i

U

i

W

NC

You toss a 0.150-kg

baseball straight upward

so that it leaves your hand

moving at 20.0 m/s. The

ball reaches a maximum

height y

2

What is the speed of the

ball when it is at a height

of y

2

/2? Ignore air

resistance.

A. 10.0 m/s

B. less than 10.0 m/s but more than zero

C. more than 10.0 m/s

D. not enough information given to decide

• Figure 7.

The graph shows the potential energy U for a particle that moves along the x -axis. The particle is initially at x = x 4 and moving in the negative x -direction. At which of the labeled points does the particle have the greatest speed? A. at x = x 1 B. at x = x 2 C. at x = x 3 D. at x = x 4 E. more than one of the above

Q7.

x O U x 1 x 2 x 3 x 4

The graph shows the potential energy U for a particle that moves along the x -axis. At which of the labeled values of x is there zero force on the particle? A. at both x = x 1 and x = x 3 B. at x = x 2 only C. at x = x 4 only D. at both x = x 2 and x = x 4

Q7.

x O U x 1 x 2 x 3 x 4

Assume a non-linear spring. Calculate velocity for non- linear and linear springs for:

F=−k x−k

2

x

2

k= 10

N

m

k

2

N

m

2

x=0.01 m

x=0.1 m

x=0.2 m

6-67 How much power is needed to push a 50 kg chest at 0.8 m/s along a horizontal floor where the coefficient of friction is 0.25? Express your answer using two significant figures. How much work is done in pushing the chest 13 m? Clicker Estimate your power consumption as you do deep knee-bends at 1 /second 6-40 In midday sunshine, solar energy strikes Earth at the rate of about 1 ( kW/m^2). (a) How long would it take a perfectly efficient solar collector of 15 m^2 area to collect 40 kW- h of energy? Note: This is roughly the energy content in a gallon of gasoline. 5-48 A 300-g paperback book rests on a 1.2-kg textbook. A force is applied to the textbook, and the two books accelerate together from rest to 1 m/s in 0.5 s. The textbook is then brought to a stop in 0.33 s, during which time the paperback slides off. Within what range does the coefficient of static friction between the two books lie? P ave =  W  t P ave  t=W 1000 W× 3600 s= 1 kW−h

A. 100 N

B. 200 N

C. 500 N

D. 1000 N

E. 2000 N

You can use work in a statics problem

Suppose you want to ride your mountain bike up a steep hill. Two paths lead from the bottom to the top, one twice as long as the other. Compared to the average force you would exert if you took the short path, the average force you exert along the longer path is A. Four times as small B. Three times as small C. Half as small D. The same E. Undetermined – It depends on the time taken.