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3 years ago

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A 58-kg skater is standing still in front of a wall. By pushing against the wall she propels herself backward with a velocity of

-1 m/s. Her hands are in contact with the wall for 0.80 s. Ignore friction and wind resistance. Find the magnitude and direction of the average force she exerts on the wall (which has the same magnitude, but opposite direction, as the force that the wall applies to her).

1 answer:

masha68 [24]3 years ago

5 0

Answer:

F = -72.5 N

Explanation:

You can do this excercise in two ways.

The first way is using the second law of Newton which is:

F = m*a

You should calculate the acceleration and then solve for F.

The second way is to use the formula of momentum which is:

F*t = m*V

Here, you only need to put the data of the excercise and solve for F.

Either way you do this, you'll get the same result.

I'll do it by both methods to prove it:

First method:

Assuming that the innitial speed is 0 (because is standing still) acceleration would be:

a = Vf/t

Solving for a:

a = -1/0.8 = -1.25 m/s^2

Now, let's solve for F:

F = 58 * (-1.25) = -72.5 N

Second method:

We know that F*t = m*V so:

F = m*V/t

F = 58 * (-1) / 0.8

F = -72.5 N

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Given:

density of air at inlet, $\rho_{a} = 1.20 kg/m_{3}$

density of air at inlet, $\rho_{b} = 1.05 kg/m_{3}$

Solution:

Now,

$\dot{m} = \dot{m_{a}} = \dot{m_{b}}$

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where

A = Area of cross section

$v_{a}$ = velocity of air at inlet

$v_{b}$ = velocity of air at outlet

Now, using eqn (1), we get:

$\frac{v_{b}}{v_{a}} = \frac{\rho_{a}}{\rho_{b}}$

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3 years ago

Read 2 more answers

Estimate humanity’s current consumption of energy in one day (in Joule).

Alex73 [517]

Based on data from world energy consumption, the estimated humanity’s current consumption of energy in one day is above 208 million joules per day.

<h3>What is energy consumption?</h3>

Energy is the ability to do work. Therefore, energy consumption refers to the amount of energy used to do work.

Humans need energy for various purposes such as;

lighting
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Due to rapid growth on population as well as technology, the human energy consumption is on the increase.

In 2020, the world primary energy consumption was 71,4 GJ per person for a world population of about 7.7 billion people.

Therefore, the estimated humanity’s current consumption of energy in one day is above 208 million joules per day.

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2 years ago

If the only forces acting on a 2.0kg mass are F1 = (3i-8j)N and F2 = (5i+3j)N, what is the magnitude of the acceleration of the

belka [17]

Answer: 4.7m/s²

Explanation:

According to newton's first law,

Force = mass × acceleration

Since we are given more the one force, we will take the resultant of the two vectors.

Mass = 2.0kg

F1+F2 = (3i-8j)+(5i+3j)

Adding component wise, we have;

F1+F2 = 3i+5i-8j+3j

F1+F2 = 8i-5j

Resultant of the sum of the forces will be;

R² = (8i)²+(-5j)²

Since i.i = j.j = 1

R² = 8²+5²

R² = 64+25

R² = 89

R = √89

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Substituting in the formula

F = ma

9.4 = 2a

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a = 4.7m/s²

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so we will have

$E = 5.14 \times 10^{11} N/C$

so above is the electric field due to proton

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