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Mrac [35]
3 years ago
10

In which one of the following situations is zero net work done? A) A ball rolls down an inclined plane. B) A physics student str

etches a spring. C) A projectile falls toward the surface of Earth. D) A box is pulled across a rough floor at constant velocity. E) A child pulls a toy across a rough surface causing it to accelerate.
Physics
2 answers:
spayn [35]3 years ago
8 0

Answer:

D

Explanation:

I have taken the test and yeah love ya

lidiya [134]3 years ago
6 0

Answer:

Option D

Explanation:

The work done can be given by the mechanical energy used to do work, i.e., Kinetic energy and potential energy provided to do the work.

In all the cases, except option D, the energy provided to do the useful work is not zero and hence work done is not zero.  

In option D, the box is being pulled with constant velocity, making the acceleration zero and thus Kinetic energy of the system is zero. Hence work done in this case is zero.

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An electric pole casts a shadow of 24 m long . If the tip of the shadow is 25m far from the top of the pole , how high is the po
Vikentia [17]

Answer:

7 m

Explanation:

a^ + b^=c^

a^ + 24^=25^

a^+576=625

a^=625-576

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7 0
3 years ago
Which of these helps you understand what people are saying to you? A. Interrupting them B. Looking away while they're speaking C
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I believe the answer is <span> D. Thinking about what they're saying
Interrupting them will make them unable to finish their full message/thought to you. Looking away while they're speaking will make you reduce your attention and unable to process the information properly. Thinking about how you'll response also limit your attention to them and could make you cloud your opinion and misinterpret what's they're saying.</span>
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3 years ago
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1. seesaw
Sergeeva-Olga [200]

Answer:

1  seesaw = first class lever

2. pencil and sharpener = wheel and axle

3. bottle opener = second class lever

4. forearm = third class lever

5. nail = wedge

Explanation:

The given objects are classic examples of simple machines.

Lever: There are 3 types of levers and they depend on where the load, applied force, and fulcrum are.

First class levers have the fulcrum in between the load and the applied force. In other words, the load and applied force are at opposite ends. The seesaw is a good example of this. Other examples would be, pliers, scissors, and the like.

Second class levers have the fulcrum and the applied force at the opposite ends. So in this case, the load is found in between. Examples of this would be a bottle opener or a crowbar.

For third class levers, the load and the fulcrum are at opposite ends and the applied force is in between. The forearm is a good example, so is a stapler, or even a broom.

A wedge is another simple machine. It is thick at one end and it gets thinner towards the other end, or it usually has a sharp end. Other examples of this would be an axe, or a knife.

A sharpener is actually a compound machine. The old-fashioned type of pencil sharpener, the one you crank makes use of a wheel and axle and a wedge. A wheel and axle is usually a machine that makes use of two circular parts; a wheel and a rod that is attached to its center.

4 0
3 years ago
A liquid flowing from a vertical pipe has a very definite shape as it flows from the pipe. To get the equation for this shape, a
Eva8 [605]
Calculating speed as function of distance y is fairly easy. Once water leaves pipe it is under free fall which means that it is accelerating with gravitational acceleration "a".
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Vff = t*a =  \sqrt{2ay}
V = Vo +  \sqrt{2ay}

Calculating radius of stream is a little bit more complicated. Because water is accelerating as it falls it has to lower its radius. The reason for this is that water flow must be the same as one at the exit of pipe. Water flow is expressed in  liters/meter^3
Because of this we write condition:
V1/V2 = A2/A1 where  A2 and A1 are sections of water stream.
let V1 and A1 be the speed and section of water stream at the end of pipe.
A2 = V1*A1/V2

r^{2}  = \frac{Vo*  r_{0} ^{2} }{Vo+ \sqrt{2ay} }
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3 years ago
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