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3 years ago

Which of the following is a chemical change?

Physics

2 answers:

e-lub [12.9K]3 years ago

4 0

A screw driver rusting when left in a pail of water is a chemical reaction

Kisachek [45]3 years ago

4 0

Answer:

a screwdriver rusting when left in a pail of water

Explanation:

In case of chemical change we can say that there must be a chemical reaction due to which there will be a change in the chemical reactants.

As we can see the given options

1). wind breaking down a rock into smaller pieces

There is no chemical reaction between them and it just a physical change of big size to smaller size

2). a leaf falling off of a tree during a storm

As we know that here also leaf detach from the tree so there is only physical change again.

3). a screwdriver rusting when left in a pail of water

Here we will have a chemical change due to which iron made its oxide due to chemical reaction of iron and oxygen

4). a block of ice melting in the sun

This is also physical change in which water molecules change from its solid state to liquid state

So here correct answer will be

a screwdriver rusting when left iwind breaking down a rock into smaller pieces

a leaf falling off of a tree during a storm

a screwdriver rusting when left in a pail of water

a block of ice melting in the sunwind breaking down a rock into smaller pieces

a leaf falling off of a tree during a storm

a screwdriver rusting when left in a pail of water

a block of ice melting in the sunwind breaking down a rock into smaller pieces

a leaf falling off of a tree during a storm

<em>a screwdriver rusting when left in a pail of water </em>

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The elastic energy stored in your tendons can contribute up to 35 % of your energy needs when running. Sports scientists have st

irina [24]

Complete Question:

The elastic energy stored in your tendons can contribute up to 35 % of your energy needs when running. Sports scientists have studied the change in length of the knee extensor tendon in sprinters and nonathletes. They find (on average) that the sprinters' tendons stretch 43 mm , while nonathletes' stretch only 32 mm . The spring constant for the tendon is the same for both groups, $31 {\rm {N}/{mm}}$ . What is the difference in maximum stored energy between the sprinters and the nonathlethes?

Answer:

$\triangle E = 12.79 J$

Explanation:

Sprinters' tendons stretch, $x_s = 43 mm = 0.043 m$

Non athletes' stretch, $x_n = 32 mm = 0.032 m$

Spring constant for the two groups, k = 31 N/mm = 3100 N/m

Maximum Energy stored in the sprinter, $E_s = 0.5kx_s^2$

Maximum energy stored in the non athletes, $E_m = 0.5kx_n^2$

Difference in maximum stored energy between the sprinters and the non-athlethes:

$\triangle E = E_s - E_n = 0.5k(x_s^2 - x_n^2)\\\triangle E = 0.5*3100* (0.043^2 - 0.032^2)\\\triangle E = 0.5*31000*0.000825\\\triangle E = 12.79 J$

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4 years ago

A circular loop of wire with radius r=0.0250 m and resistance r=0.390 ohms is in a region of spatially uniform magnetic field. t

slavikrds [6]

Answer:

0.0133 A

Explanation:

The time at which B=1.33 T is given by

1.33 = 0.38*t^3

t = (1.33/0.38)^(1/3) = 1.52 s

Using Faraday's Law, we have

emf = - dΦ/dt = - A dB/dt = - A d/dt ( 0.380 t^3 )

Area A = pi * r² = 3.141 *(0.025 *0.025) = 0.00196 m²

emf = - A*(3*0.38)*t^2

thus, the emf at t=1.52 s is

emf = - 0.00196*(3*0.38)*(1.52)^2 = -0.0052 V

if the resistance is 0.390 ohms, then the current is given by

I = V/R = 0.0052/0.390 = 0.0133 A

3 0

3 years ago

Which best describes the law of conservation of mass?

Sergio039 [100]

Explanation:

The law of conservation of mass states that mass in an isolated system is neither created nor destroyed by chemical reactions or physical transformations. According to the law of conservation of mass, the mass of the products in a chemical reaction must equal the mass of the reactants.

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3 years ago

What is the potential energy of a 2500 g object suspended 5 m above the earth's surface?

alexandr402 [8]

Answer:

Explanation:

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P.E = m × g × h

Where;

m = mass (kg)

g = acceleration due to gravity (10m/s²)

h = height (m)

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