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zubka84 [21]
3 years ago
11

a stone is dropped from the top of 50 m high tower simultaneously another stone is thrown upward with a speed of 20 m/s . calcul

ate the time at which both the stones cross each other
Physics
1 answer:
Darina [25.2K]3 years ago
7 0
'H' = height at any time
'T' = time after both actions
'G' = acceleration of gravity
'S' = speed at the beginning of time
Let's call 'up' the positive direction.
Let's assume that the tossed stone is tossed from the ground, not from the tower.

For the stone dropped from the 50m tower:

H = +50 - (1/2) G T²

For the stone tossed upward from the ground:

H = +20T - (1/2) G T²

When the stones' paths cross, their <em>H</em>eights are equal.

50 - (1/2) G T² = 20T - (1/2) G T²

Wow !  Look at that !  Add (1/2) G T² to each side of that equation,
and all we have left is:

50 = 20T  Isn't that incredible ? ! ?

Divide each side by 20 :

<u>2.5 = T</u>

The stones meet in the air 2.5 seconds after the drop/toss.

I want to see something: 
What is their height, and what is the tossed stone doing, when they meet ?

Their height is  +50 - (1/2) G T² = 19.375 meters

The speed of the tossed stone is  +20 - (1/2) G T = +7.75 m/s ... still moving up.
I wanted to see whether the tossed stone had reached the peak of the toss,
and was falling when the dropped stone overtook it.  The answer is no ... the
dropped stone was still moving up at 7.75 m/s when it met the dropped one.
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2 years ago
Which of the following sets of properties leads to a high degree of thermal shock resistance? (A) High fracture strength High th
Rina8888 [55]

Answer:  

The correct Answer is C) <u>High fracture strength,</u> <u>High Thermal Conductivity,</u> <u>Low modulus of elasticity,</u> <u>Low coefficient of thermal</u>                                                                                                                                                                                                                                              

Explanation:

The ability of a solid to withstand sudden changes in temperature either during heating or cooling is known or referred to as Thermal Shock Resistance (TSR).

Thermal shock resistance is one of the most crucial factors of performance in solids for high temperature environments that can cause thermal stresses and risks for thermal shock damage.

Examples are as of such environments are energy conversion systems, electronic devices and cutting tools.

A common way to evaluate TSR is to look for maximum jump in surface temperature which a material can sustain without cracking.  This is known as thermal conductivity.

Failure due to thermal shock can be prevented by;

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  • Reducing the material's coefficient of thermal expansion
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  • Introducing built-in compressive stress, as for example in tempered glass and in some cases tempered plastic
  • reducing its Young's modulus
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Thermal conductivity is an intensive physical property of a material that relates the heat flow through the material per unit area to temperature gradient across the material. The thermal conductivity of a material is basically a measure of its ability to conduct heat.    

The other factor that contributes to a high degree of thermal shock is:

Fracture Strength: This is the ability of a material containing a crack to resist fracture or resist becoming brittle. For example, glass has a high strength, but the presence of a small fracture reduces the strength. Therefore, glass has low fracture resistance. Fracture toughness is an important consideration in hydraulic fracture design.

Modulus of Elasticity:

An object or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it is calculated  or measured by a quantity known as Elastic Modulus (also known as Young modulus of elasticity)

A stiff material has a high Young's modulus and changes its shape only slightly under elastic loads (e.g. steel or diamond). A flexible material has a low Young's modulus and changes its shape considerably (e.g. rubbers).

Coefficient of thermal expansion (CTE) this refers to how the rate of change in the  size of an object with respect of every degree change in temperature assuming that pressure remains the same. An object with low CTE is Fine Ceramics or Advanced Ceramics.

Cheers!

               

4 0
3 years ago
A stone is thrown from the top of a building 30m high. If it strikes the ground at an angle 45, with what speed was it thrown?
sasho [114]

Answer:

24.2 m/s

Explanation:

The stone strikes the ground at an angle of 45 degrees: this means that its vertical velocity is equal (in magnitude) to its horizontal velocity, in fact:

tan \theta = \frac{|v_y|}{v_x}\\tan 45^{\circ} = 1 \rightarrow |v_y| = v_x

The motion along the vertical direction is a uniformly accelerated motion, so we can find the final vertical velocity using the following suvat equation

v_y^2 -u_y^2 = 2as

where

v_y is the final vertical velocity

u_y = 0 is the initial vertical velocity (zero because the stone is thrown horizontally)

a=g=9.8 m/s^2 is the acceleration of gravity (we take downward as positive direction)

s = 30 m is the vertical displacement

Solving for vy,

v_y = \sqrt{u_y^2+2as}=\sqrt{0+2(9.8)(30)}=24.2 m/s

This means that the horizontal velocity is also 24.2 m/s: and since the horizontal velocity is constant during the whole motion (there is no acceleration in the horizontal direction), this means that the stone was thrown exactly at 24.2 m/s.

7 0
3 years ago
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