21. Which object would most likely be made of a material that is a thermal conductor?

A bungee jumper of mass 75kg is attached to a bungee cord of length L=35m. She walks oﬀ a platform (with no initial speed), reac

attashe74 [19]

Answer:

1. 77.31 N/m

2. 26.2 m/s

3. increase

Explanation:

1. According to the law of energy conservation, when she jumps from the bridge to the point of maximum stretch, her potential energy would be converted to elastics energy. Her kinetic energy at both of those points are 0 as speed at those points are 0.

Let g = 9.8 m/s2. And the point where the bungee ropes are stretched to maximum be ground 0 for potential energy. We have the following energy conservation equation

$E_P = E_E$

$mgh = kx^2/2$

where m = 75 kg is the mass of the jumper, h = 72 m is the vertical height from the jumping point to the lowest point, k (N/m) is the spring constant and x = 72 - 35 = 37 m is the length that the cord is stretched

$75*9.8*72 = 37^2k/2$

$k = (75*9.8*72*2)/37^2 = 77.31 N/m$

2. At 35 m below the platform, the cord isn't stretched, so there isn't any elastics energy, only potential energy converted to kinetics energy. This time let's use the 35m point as ground 0 for potential energy

$mv^2/2 = mgH$

where H = 35m this time due to the height difference between the jumping point and the point 35m below the platform

$v^2/2 = gH$

$v = \sqrt{2gH} = \sqrt{2*9.8*35} = 26.2 m/s$

3. If she jumps from her platform with a velocity, then her starting kinetic energy is no longer 0. The energy conservation equation would then be

$E_P + E_k = E_E$

So the elastics energy would increase, which would lengthen the maximum displacement of the cord

5 0

4 years ago

If the specific latent heat of ice is 340 000 J/kg,

Ganezh [65]

Answer:

jsjdgsudgwid s

Explanation:

83638hr is 3738 so 8273 and 837y37 and 82638 say hi to 1937

6 0

3 years ago

Two objects moving with a speed v travel in opposite directions in a straight line. The objects stick together when they collide

shutvik [7]

Answer:

A. K1/K2 = 36

B. M/m = 7/5

Explanation:

Part A. In order to calculate the ratio of the final kinetic energy and the initial kinetic energy of the system, you first express the kinetic energy of the system before and after the collision.

Before the collision:

$K_1=\frac{1}{2}Mv^2+\frac{1}{2}mv^2=\frac{1}{2}(M+m)v^2$ (1)

After the collision:

$K_2=\frac{1}{2}(M+m)(\frac{v}{6})^2=\frac{1}{72}(M+m)v^2$ (2)

The quotient between K1 and K2 is given by:

$\frac{K_1}{K_2}=\frac{1/2(M+m)v^2}{1/72(M+m)v^2}=\frac{1/2}{1/72}=36$

The quotient between the kinetic energy before and after the collision is K1/K2 = 36

Part B. To find the relation between the masses you use the momentum conservation law. The total momentum of the system before the collision and after the collision is given by:

$Mv-mv=(m+M)(\frac{v}{6})$ (3)

Where the minus sign in the first member of the equation means that the direction of the motion of both objects are opposite between them.

From the previous equation you can cancel the speed v and solve for M/m:

$(M-m)v=(m+M)(\frac{v}{6})\\\\M-m=\frac{1}{6}(m+M)\\\\M-\frac{1}{6}M=\frac{1}{6}m+m\\\\\frac{5}{6}M=\frac{7}{6}m\\\\\frac{M}{m}=\frac{7}{5}$

The ratio M/m is equal to 7/5

6 0

3 years ago

An ore car of mass 39000 kg starts from rest and rolls downhill on tracks from a mine. At the end of the tracks, 19 m lower vert

cupoosta [38]

Answer:

The compression in the spring is 5.88 meters.

Explanation:

Given that,

Mass of the car, m = 39000 kg

Height of the car, h = 19 m

Spring constant of the spring, $k=4.2\times 10^5\ N/m$

We need to find the compression in the spring in stopping the ore car. It can be done by balancing loss in gravitational potential energy and the increase in elastic energy. So,

$mgh=\dfrac{1}{2}kx^2$

x is the compression in spring

$x=\sqrt{\dfrac{2mgh}{k}} \\\\x=\sqrt{\dfrac{2\times 39000\times 19\times 9.8}{4.2\times 10^5}} \\\\x=5.88\ m$

So, the compression in the spring is 5.88 meters.

6 0

3 years ago

The farther the object is stretched or compressed, the greater its potential energy.

lord [1]

True, think of a rubber band, the more it is stretched the more potential energy that when you let go can be turned into more kinetic energy than if you had less tension on the rubber band.

6 0

3 years ago