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3 years ago

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A rock weighing 98 newtons is pushed off the edge of a bridge 50 meters above the ground. What was the potential energy of the r

ock before it began to fall?

2 answers:

barxatty [35]3 years ago

5 0

<u>Answer:</u> The potential energy of the rock before it began to fall is 4900 J

<u>Explanation:</u>

Force is defined as the mass multiplied by the acceleration of the object.

$F=mg$

where,

F = force exerted on the object

m = mass of the object

g = acceleration due to gravity

Potential energy is defined as the energy possessed due to the height of the object.

Mathematically,

$E_p=mgh$

Or,

$E_p=F\times h$

where,

$E_p$ = potential energy of the rock = ?

F = force applied on the rock = 98 N

h = height of the bridge from where the rock is thrown = 50 m

Putting values in above equation, we get:

$E_p=98N\times 50m\\\\E_p=4900J$

Hence, the potential energy of the rock before it began to fall is 4900 J

lidiya [134]3 years ago

4 0

Ep = 4900 because Ep = wh

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An object thrown in the air has a velocity after t seconds that can be described by v(t) = -9.8t + 24 (in meters/second) and a h

marin [14]

Answer and Explanation: Kinetic energy is related to movement: it is the energy an object possesses during the movement. it is calculated as:

$K=\frac{1}{2}mv^{2}$

For the object thrown in the air:

$K=\frac{1}{2}.2.[v(t)]^{2}$

$K=(-9.8t+24)^{2}$

$K=96.04t^{2}-470.4t+576$

Kinetic energy of the object as a function of time: $K=96.04t^{2}-470.4t+576$

Potential energy is the energy an object possesses due to its position in relation to other objects. It is calculated as:

$U=mgh$

For the object thrown in the air:

$U=9.8.2.h(t)$

$U=9.8.2.(-4.9t^{2}+24t+60)$

$U=-96.04t^{2}+470.4t+1176$

Potential energy as function of time: $U=-96.04t^{2}+470.4t+1176$

Total kinetic and potential energy, also known as mechanical energy is

TME = $96.04t^{2}-470.4t+576$ + ( $-96.04t^{2}+470.4t+1176$ )

TME = 1752

The expression shows that total energy of an object thrown in the air is constant and independent of time.

6 0

3 years ago

A 1-kg block is lifted vertically 1 m at constant speed by a boy. The work done by the boy is about:

Igoryamba

Answer:

$9.8\; {\rm J}$ , assuming that the gravitational field strength is $g = 9.8\; {\rm N \cdot kg^{-1}}$ .

Explanation:

Notice that both the speed and the direction of motion of this block are constant. In other words, the velocity of this block is constant.

By Newton's Second Law, the net force on this block would be $0$ . External forces on this block should be balanced. Thus, the magnitude of the (downward) weight of this block should be equal to the magnitude of the (upward) force that the boy applies on this block.

Let $m$ denote the mass of this block. It is given that $m = 1\; {\rm kg}$ . The weight of this block would be:

$\begin{aligned}\text{weight} &= m\, g \\ &= 1\; {\rm kg} \times 9.8\; {\rm N \cdot kg^{-1}} \\ &= 9.8\; {\rm N}\end{aligned}$ .

Hence, the force that the boy applies on this block would be upward with a magnitude of $F = 9.8\; {\rm N}$ .

The mechanical work that a force did is equal to the product of:

the magnitude of the force, and
the displacement of the object in the direction of the force.

The displacement of this block (upward by $s = 1\; {\rm m}$ ) is in the same direction as the (upward) force that this boy had applied. Thus, the work that this boy had done would be the product of:

the magnitude of the force that this boy exerted, $F = 9.8\; {\rm N}$ , and
the displacement of this block in the direction, $s = 1\; {\rm m}$ .

$\begin{aligned}\text{work} &= F\, s \\ &= 9.8\; {\rm N} \times 1\; {\rm m} \\ &= 9.8\; {\rm J}\end{aligned}$ .

5 0

2 years ago

Indigenous people sometimes cooked in watertight baskets by placing enough hot rocks into the water to bring it to a boil. What

yaroslaw [1]

Answer:

The rock has a mass of 4.02 kg

Explanation:

<u>Step 1: </u>Data given

Mass of the rock = TO BE DETERMINED

Temperature of the rock = 500 °C

Mass of the water =4.24 kg

⇒ loses 0.044kg as vapor

Initial temperature of the water = 29°C

Final temperature = 100°C

Specific heat of rock = 0.20 kcal/kg °C

Specific heat of water = 1kcal/kg°C

Latent heat of vaporization = 539 kcal/kg

<u>Step 2:</u> formules

Qlost,rock + Qgained,water = 0

Qtotal,water = Qwater +Qvapor

<u>Step 3: </u>Calculate Qvapor

Qvapor = mass of vapor * Latent heat of vapor

Qvapor = 0.044kg * 539 kcal/kg = 23.716 kcal

<u>Step 4: </u>Calculate Qwater

Qwater = mass of water * specific heat * Δtemperature

Qwater = 4.196 kg * 1kcal/kg°C *( 100-29)

Qwater = 297.916 kcal

<u>Step 5:</u> Calculate Qwater,total

Qwater,total = Qwater + Qvapor

Qwater,total = 23.716 kcal + 297.916 = 321.632 kcal

<u>Step 6</u>: Calculate Qrock

Qrock = mass of rock * specific heat rock * Δtemperature

Qrock = mass of rock * 0.20 kcal/kg°C * (100-500)

Qrock = mass of rock * -80 kcal/kg

<u>Step 7:</u> Calculate mass of rock

Qlost,rock + Qgained,water = 0

Qlost,rock = -Qgained,water

mass of rock * -80 kcal/kg = -321.632 kcal

mass of rock = 4.02 kg

The rock has a mass of 4.02 kg

7 0

3 years ago

Which equation describes the sum of the vectors plotted below?

bearhunter [10]

Equation C describes the sum of the vectors plotted below.

<h3>What is a vector?</h3>

A vector is a quantity or phenomena with magnitude and direction that are independent of one another. The phrase also refers to a quantity's mathematical or geometrical representation.

If no vector can be written as a linear combination of the others, a set of vectors is said to be linearly independent.

The given points from the graph is obtained as;

a = (2,1)

b = (3,-2)

Vector, OA = 2x + y

Vector, AB = x - 3 y

From the triangular lawe of the vector addition;

$\rm r= \vec{OA} +\vec{OB}\\\\\ r= 2x+y+x-3y \\\\ r= 3x-2y$

Hence,option C is correct.

To learn more about the vector refer to the link;

brainly.com/question/13322477

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2 years ago

Boat A and Boat B have the same mass. Boat A's velocity is three times greater than that of Boat B. Compared to

Zarrin [17]

Answer:

nine times as much.

Explanation:

K.E of A = 9 times K.E of B

7 0

3 years ago

Read 2 more answers