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madam [21]
3 years ago
15

A heat engine does 9200 J of work per cycle while absorbing 22.0 kcal of heat from a hightemperature reservoir. What is the effi

ciency of this engine?
Physics
1 answer:
Morgarella [4.7K]3 years ago
4 0

Answer: 9.9%

Explanation: efficiency = (work output /work input) × 100

Note that, 1 kilocalorie = 4184 joules, hence 22kcal = 22× 4184 = 92048 joules.

Work output = 9200 j and work input = 92048 j

Efficiency = (9200/92048) × 100 = 0.099 × 100 = 9.9%

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A bobsledder pushes her sled across horizontal snow to get it going, then jumps in. After she jumps in, the sled gradually slows
anastassius [24]

Answer:

In the vertical direction the acting forces are the normal force and the weight of the bobsleder plus the sled. In the horizontal direction the acting force is the friciton force.

Explanation:

Hi there!

Please, see the attached figure for a graphic representation of the forces acting on the sled after the bobsleder jumped in.

In the vertical direction, the acting forces are the normal force (N) and the weight of the sled plus the bobsledder (W).

Since the sled is not being accelerated in the vertical direction, the sum of forces in that direction is zero:

∑Fy = W + N = 0 ⇒ W = N

The weight is calculated as follows:

W = (mb + ms) · g

Where:

mb = mass of the bobsleder.

ms = mass of the sled.

g = acceleration due to gravity.

In the horizontal direction the only acting force is the friction force (Fr). The friction force is calculated a follows:

Fr = N · μ

Where:

N = normal force.

μ = kinetic friction coefficient.

Since N = W = (mb + ms) · g

Fr = (mb + ms) · g · μ

If we want to find the acceleration of the sled after the bobsleder jumps in, we can apply Newton's second law:

∑F = m · a

Where "a" is the acceleration and "m" is the mass of the object (in this case, the mass of bobsleder plus the mass of the sled).

∑F = Fr =  (mb + ms) · g · μ =  (mb + ms) · a

(mb + ms) · g · μ =  (mb + ms) · a

Solving for "a":

g · μ = a

3 0
3 years ago
The first transistor, made of gold, plastic, and germanium (a metallic
Citrus2011 [14]

The first transistor made of gold, plastic and germanium was about the size of adult's fingernail.

Option C

<u>Explanation:</u>

The first transistor made of gold, plastic and germanium was invented in Bell laboratories. It is termed as point contact transistor. As it is made like a pointed arrow with both the sides covered with layer of gold foil. The germanium is used at the tip, just like the base and the gold foil ends as collector and emitter.

The size of this transistor is about the size of adult's fingernail. It is very small in size and it was one of its kind. Due to this small size and the working capacity by the point contact, it is termed as point contact transistor.

3 0
3 years ago
For a certain optical medium the speed of light varies from a low value of 1.90 × 10 8 m/s for violet light to a high value of 2
Dmitry_Shevchenko [17]

Answer:

a. The refractive index ranges from 1.5 - 1.56

b. 18.7° for violet light and 19.5° for red light.

c. 33.7° for violet light and 35.3° for red light.

Explanation:

a. The refractive index of an object is the ratio of the speed of light in a vacuum and the speed of light in the object.

Mathematically,

n = \frac{c}{v}

The speed of violet light in the object is 1.9 * 10^8 m/s.

The speed of red light in the object is 2 * 10^8 m/s

Hence, the refractive index for violet light is:

n = \frac{3 * 10^8 }{1.9 * 10^8} \\\\n = 1.56

and for red light, it is:

n = \frac{3 * 10^8 }{2 * 10^8} \\\\n = 1.5

Hence, the refractive index ranges from 1.5 - 1.56.

b. The refractive index is also the ratio of the sine of the angle of incidence to the sine of the angle of refraction.

n = \frac{sin(i)}{sin(r)}

The angle of incidence is 30°.

The angle of refraction for violet light will be:

1.56 = \frac{sin(30)}{sin(r)}\\ \\sin(r) = \frac{sin(30)}{1.56}  = \frac{0.5}{1.56} \\\\sin(r) = 0.3205\\\\r = 18.7^o

And the angle of refraction for red light will be:

1.5 = \frac{sin(30)}{sin(r)}\\ \\sin(r) = \frac{sin(30)}{1.5}  = \frac{0.5}{1.5} \\\\sin(r) = 0.3333\\\\r = 19.5^o

The angle of refraction for red light is larger than that of violet light when the angle of incidence is 30°.

c. The angle of incidence is 60°.

The angle of refraction for violet light will be:

1.56 = \frac{sin(60)}{sin(r)}\\ \\sin(r) = \frac{sin(60)}{1.56}  = \frac{0.8660}{1.56} \\\\sin(r) = 0.5551\\\\r = 33.7^o

And the angle of refraction for red light will be:

1.5 = \frac{sin(60)}{sin(r)}\\ \\sin(r) = \frac{sin(60)}{1.5}  = \frac{0.8660}{1.5} \\\\sin(r) = 0.5773\\\\r = 35.3^o

The angle of refraction for red light is still larger than that of violet light when the angle of incidence is 60°.

6 0
3 years ago
An airplane in the process of taking off travels with a speed of 80 m/s at an angle of 15° above the horizontal. What is the gro
9966 [12]

Answer:

Option C

Explanation:

given,

velocity of airplane = 80 m/s

angle with the horizontal = 15°

speed of the ground= ?

when the plane is taking off the horizontal component of the velocity is v cosθ

so,      

        ground speed of the airplane is = v\times cos\theta

                                                              = 80 \times cos 15^0

                                                           v  =  77.27 m/s

horizontal velocity of the air plane comes out to be 77.27 m/s ≅ 77 m/s

so, the correct option is Option C

5 0
3 years ago
What is the minimum force required to increase the energy of a car by 68 j over a distance of 12 m? Assume the force is constant
g100num [7]
The wording of this can be bothersome. I think you should be using
E = F * d
E = 68 J
d = 12 m
F = ???

68J = F * 12 m
68J/12 m = F
5.67 N

A <<<<<====== Answer

3 0
3 years ago
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