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natta225 [31]
3 years ago
12

sharpening a pencil leaves behind pencil shavings. is sharpening a pencil a physical change or a chemical change

Physics
1 answer:
Alja [10]3 years ago
7 0
It is a physical change 
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A hair dryer uses 1200 watts of power. Current flow through
KonstantinChe [14]
The answer is: 120V

Power is the rate at which energy is supplied/transformed in time:
we can write:

V ddp in Volts represents Energy/Charge i.e. energy carried by each coulomb;

I current in Amperes represents Charge/time or coulombs passing each seconds.

combining them we have:

Power = energy/time = V • 1

or

1200 = V ⋅ 10
V = 1200/10 = 120V
6 0
3 years ago
Read 2 more answers
A boy is pulling a load of 150N with a string inclined at an angle 30 to the horizontal if the tension of string is 105N the for
Lorico [155]

The force tending to lift the load (vertical force) is equal to <u>22.5N.</u>

Why?

Since the boy is pulling a load (150N) with a string inclined at an angle of 30° to the horizontal, the total force will have two components (horizontal and vertical component), but we need to consider the given information about the tension of the string which is equal to 105N.

We can calculate the vertical force using the following formula:

VerticalForce=Force*Sin(30\° )=(BoysForce-StringForce)*\frac{1}{2}\\\\VerticalForce=(150N-105N)*\frac{1}{2}=VerticalForce=45N*\frac{1}{2}=22.5N

Hence, we can see that <u>the force tending to lift the load</u> off the ground (vertical force) is equal to <u>22.5N.</u>

Have a nice day!

8 0
3 years ago
While Bob is demonstrating the gravitational force on falling objects to his class, he drops an 1.0 lb bag of feathers from the
____ [38]

As per the question Bob drops the bag full with feathers from the top of the building.

The mass of the bag(m)= 1.0 lb

Let the air resistance is neglected.As the bag is under free fall ,hence the only force that acts on the bag is the force of gravity which is in vertical downward direction.

Here the acceleration produced on bag due to the free fall will be nothing else except the acceleration due to gravity i.e g =9.8 m/s^2


Here we are asked to calculate the distance travelled by the bag at the instant 1.5 s

Hence time t= 1.5 s

From equation of kinematics we know that -

                S=ut + 0.5at^2     [ here S is the distance travelled]

For motion under free fall initial velocity (u)=0.

Hence   S= 0×1.5+{0.5×(-9.8)×(1.5)^2}

           ⇒ -S =0-11.025 m

            ⇒ S= 11.025 m

                   =11 m

Here the negative sign is taken only due to the vertical downward motion of the body .we may take is positive depending on our frame of reference .


Hence the correct option is B.

               

3 0
3 years ago
Read 2 more answers
A kite 100 ft above the ground moves horizontally at a speed of 12 ft/s. at what rate is the angle (in radians) between the stri
Viefleur [7K]
<span>Answer: So this involves right triangles. The height is always 100. Let the horizontal be x and the length of string be z. So we have x2 + 1002 = z2. Now take its derivative in terms of time to get 2x(dx/dt) = 2z(dz/dt) So at your specific moment z = 200, x = 100âš3 and dx/dt = +8 substituting, that makes dz/dt = 800âš3 / 200 or 4âš3. Part 2 sin a = 100/z = 100 z-1 . Now take the derivative in terms of t to get cos a (da./dt) = -100/ z2 (dz/dt) So we know z = 200, which makes this a 30-60-90 triangle, therefore a=30 degrees or Ď€/6 radians. Substitute to get cos (Ď€/6)(da/dt) = (-100/ 40000)(4âš3) âš3 / 2 (da/dt) = -âš3 / 100 da/dt = -1/50 radians</span>
5 0
3 years ago
Consider heat transfer between two identical hot solid bodies and the air surrounding them. The first solid is being cooled by a
Nitella [24]

Answer:

The solution to the question above is explained below:

Explanation:

For which solid is the lumped system analysis more likely to be applicable?

<u>Answer</u>

The lumped system analysis is more likely to be applicable for the body cooled naturally.

<em>Question :Why?</em>

<u>Answer</u>

Biot number is proportional to the convection heat transfer coefficient, and it is proportional to the air velocity. When Biot no is less than 0.1 in  the case of natural convection, then lumped analysis can be applied.

<u>Further explanations:</u>

Heat is a form of energy.

Heat transfer describes the flow of heat across the boundary of a system due to temperature differences and the subsequent temperature distribution and changes. There are three different ways the heat can transfer: conduction, convection, or radiation.

Heat transfer  analysis which utilizes this idealization is known as the lumped system analysis.

The Biot number is a criterion dimensionless quantity used in heat transfer calculations which gives a direct indication of the relative importance of conduction and convection in determining the temperature history of a body being heated or cooled by convection at its surface. In heat transfer analysis, some bodies are observed to behave like a "lump" whose entire  body temperature remains essentially uniform at all times during a heat transfer process.

Conduction is the transfer of energy in the form of heat or electricity from one atom to another within an object and conduction of heat occurs when molecules increase in temperature.

Convection is a transfer of heat by the movement of a fluid. Convection occurs within liquids and gases between areas of different temperature.

7 0
3 years ago
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