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# Is a pencil sharpener a first class lever?

no it is in fact a first class lever because a see-saw is first class and this is basically a see saw except instead of a handle on each side there is 2 on one side so therefore its a first class but people think it is a second class because of scissors but this a scissors have a difference and that difference it that when using scissors when you move one handle, it moves on the other side of the fulcrum but with a can opener the handles make the actual metal that opens the can move not just the same thing but on the other side

# What is the value of absorption coefficient of an open window?

Open doors and windows are considered to be completely absorptive (a=1) because all the sound waves continue traveling out the space instead of being reflective back into the room.

It should be noted that for the case of doors or windows opening into a space where another wall may reflect the sound (hallway, closet, etc.) then the absorption will be less than ideal, but still fairly significant.

# What are liquid drops or solid particles spread through gas?

A gas cannot easily pass through a liquid or a solid however it can be entrapped in it . If a gas bubble is formed in a liquid it moves upward and escapes out of the liquid. Gas cannot pass through a solid barrier.

# What is the formula for conservation of mechanical energy?

There are many equations to solve for energy, depending on what form of energy your looking at. For kinetic energy, us KE = (1/2)mv2 where KE is kinetic energy, m is mass, and v is velocity. For potential energy used PE=mgh where PE is potential energy, m is mass, g is gravity, and h is height. Mechanical energy is PE + KE. There are also numerous equations for finding the amount of thermal energy.

# What type of force does an object have if its net force is equal to zero?

If the net force on an object is zero, we can say that the forces are balanced, or that they are in equilibrium(which really means the same thing). There may be forces acting on the object, but there is an equal and opposite force pushing or pulling in the opposite direction, and all the forces balance out. Alternatively, there may be no forces acting on the object at all.

# A certain spring stretches 6 cm when a load of 15 N is suspended from it How much will the spring stretch if 30 N is suspended from it and it doesn't reach its elastic limit?

It will stretch 6 cm.

# What is an object's mass multiplied by its velocity?

mass x velocity = momentum.

(velocity = speed with a direction)

# What is magnitude in physics?

In physics, quantities can be subdivided into two groups: scalar quantities and vector quantities. A scalar quantity is a quantity with magnitude and a unit. A vector quantity is a quantity with magnitude, a unit, and a direction. Obviously, magnitude is required for both, but what exactly is magnitude?

Magnitude is simply the "size" of a quantity. Magnitudes are expressed in numerical form; e.g., 450, 0.45, 2/3, etc.

A common example of a scalar quantity is speed. If a man is driving at a speed of 50 km/h, we say the magnitude of the scalar quantity is 50. Notice that the sentence "I am driving 50" is incomplete. Therefore, the magnitude is equipped with a unit, in this case km/h (kilometres per hour).

A vector example is velocity, which is simply speed with a direction. If a plane is traveling at 240 m/s [East], then the magnitude of its velocity is 240 m/s, just like what the magnitude of its speed would be. But, since velocity is a vector, you must include the direction as well.

# What level of a lever is a bottle opener in?

It is a third class lever.

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It is a second class lever.

# What is the symbol for mass?

the answer is "m" but do not get it confused with "M" because that is a different term

# Examples of a compound machine?

Scissors

Wheelbarrow

Thats all i can think of right now

# How do levers help us do work?

it is a simple machine with a point on it called the fulcrum

# What amount of force is needed to bend metal?

Depends on what metal you are refering to. * Aluminum is can be bent at 1 ton * Stainless at 50 ton * Mild Steel at 100 tons * Carbon Steel can be bent at 150 tons. All of these metal depend on the thickness of the material. For example, the thickness of these metal would have to be between the thickness of .25 (quarter inch) to .50 (half inch). Note: It also depends of the quality of the metal. SS 1311-00 steel (Swedish standard), for example, can handle 220N per square millimetre until it reaches its yield point. Once the yield point is passed some fraction of the deformation will be permanent and non-reversible. Answer: Mathematically

Δ = PL3/(48EI) Where: Δ = deflection

L = span

E = Modulus of Elasticity (see link for typicals)

I = Moment of Inertia

b = width

d = depth

I = bd3/12 for a rectangular cross section

# Do all objects accelerate the same when they are dropped?

If we are to neglect air resistance, then yes. There is a video of the Apollo 15 astronauts putting this to the test on the moon, using a feather and a hammer. When the astronaut drops the objects, they hit the ground at the same time. The video is on YouTube.

# If a stone falls from rest and takes 16 seconds to hit the ground How tall is the ledge?

The use of more accurate figures for gravity (a) will affect the answer, as does the figure of 16 seconds which limits the significant figures of the answer.

For a = 9.8 m/sec2, the result is 1.3 x 103 meters.

For a = 9.80665 m/sec2, the result is 1255.2512 meters.

First Calculation

Using the equation

s = ut +1/2at2

Where s = displacement, u = initial velocity, a = acceleration & t = time.

Since

u = 0, t = 16s & a = 9.80665 ms2

s = (0 * 16) + (1/2 * 9.8 * 162)

s = 0 + 1255.2512

s = 1255.2512 meters

Second Calculation

First, we must assume that there is negligible air resistance. This is questionable because by analysis, one can see that the stone will be traveling quickly by the time it approaches the ground. However, it is necessary because we do not know any of the characteristics of the stone (dimensions/mass), nor the fluid resistance constant of the air.

Using a common kinematics formula, it is them possible to find the height of the ledge. Note that since the stone falls (rather than being thrown, or the like) it has an initial velocity of zero. The acceleration due to gravity used is 9.8m/s2. A rounded version of the constant is used because the question does not state whereabouts this ledge is, and acceleration due to gravity changes slightly based on where one is.

d=Vit+(1/2)*at2

d=0+(1/2)*(9.8m/s2)(16s)2

d=1254.4m

Considering significant figures, the height of the ledge is 1.2x103m.

Third Calculation

Assuming that air resistance is negligible, the ledge is 1254.4 meters tall.

Use the kinematics equation x = 0.5at2 + v0t + x0

where a stands for acceleration, t for time, v0 for initial velocity, and x0 for initial position.

We are given that v0 = 0. We can also say that the top of the ledge is x0 and that x0 = 0. Furthermore since we assumed that the only force acting on the stone is gravity, gravity is the force that will provide the acceleration. Thus, a = g = 9.8m/s2.

Putting this all together we get x = 0.5(9. 8m/s2)(16 sec)2 + (0)(16 sec) + 0 = 1254.4 m.

Note that if you are using significant figures the answer will be 1.3 x 103 m.

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# What is the net force acting on the box when the box is 15 kg and is dragged across the floor by a force of 75 N and the force of friction is 30 N?

It depends on the direction of the two forces. If the two forces are in the same direction, the net force would be 60N or -60N. If the two forces are in opposite directions the net force would be either 30N or -30N.

# Are you supposed to torque bolts or nuts?

It depends on the application, if you are speaking generally.

If you meant for applications where the bolt and nut are both present, and specific torque specifications are required, it really doesn't matter. Whichever is best accessible by the torque wrench. The only stipulation is that whichever item the torque wrench is not being used on, must be static (unable to turn). For example, if you are torquing the nut, the bolt must not be able to turn (held in place with a wrench, if necessary) while the torque wrench is being read, for a reading to be accurate.

# Can an object's velocity change direction when its acceleration is constant?

No. Acceleration is a change of velocity and doesn't have to point in the same direction. Consider braking car: it still moves with decreasing velocity in one direction, while braking force and thus acceleration is in the opposing direction.

# How many joules of kinetic energy does a 750 kg car traveling at 65 mi hr have. By what factor would its kinetic energy decreases if the car travel half as fast?

For this question, we will use the formula K = 1\2 mv2. But first, we must convert the 65 miles per hour into meters per second. Multiply miles per hour by a factor of 1.609 to get kilometers per hour. Divide this answer by 3600 to get kilometers per second. Multiply this by 1000 to get meters per second. In this case, the velocity in meters per second is aproxamitely 29 meters per second. To get the kinetic energy, we multiply one half, times the mass 750 kg, times 292 meters per second. This yields 315375 Joules. If we halved the velocity, the kinetic energy would be one-fourth that of the original kinetic energy. This is because the velocity is squared. This holds true if we go to one third the original speed. Then it would be one-ninth of the original kinetic energy.

# What is pneumatics used for?

Pneumatics is the use of pressurized air to effect mechanical motion. Pneumatics is used in a variety of different areas.For example in dentistry applications, pneumatic drills are lighter, faster, and simpler than an electric drill of the same power rating (because the prime component, the compressor, is separate from the drill and pumped air is capable of rotating the drill bit at extremely high rpm). Pneumatic transfer systems are employed in many industries to move powders and devices. Pneumatic tubes can carry objects over distances. Pneumatic devices are also used where electric motors cannot be used for safety reasons, such as deep in a mine where explosive dust or gases may be present.

# What is an angular speed of a rotating body?

Angular velocity is given as radians per second; angular speed is also the same thing. Velocity is a vector with magnitude and direction and speed a scalar with magnitude only. The magnitude is identical; velocity will define the direction of rotation ( clockwise or counterclockwise).

# What is the net force on an object at rest?

A moving object with no forces acting on it will continue to move because of inertia. For example, if the object is a chunk of rock in deep space, there will be nothing to slow it down and it might tumble for millenia. In contrast, a ball rolling across a grass field will have the force of friction from the grass (and a bit from air) slowing it down.