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faltersainse [42]

2 years ago

7

The stair stepper is a novel exercise machine that attempts to reproduce the work done against gravity by walking up stairs. Wit

h each step, Brad (of mass 60 kg) simulates stepping up a vertical distance of 0.2 m with this machine. If Brad exercises for 13 min per day with a stair stepper at a frequency of 50 steps per minute, what total work he does he do each day

1 answer:

Delicious77 [7]2 years ago

7 0

Answer:

W = 76518 J = 76.518 KJ

Explanation:

First, we will find the total number of steps taken by Brad, as follows:

$No.\ of\ steps = n = (13\ min)(50\ steps/min) = 650\ steps\\$

Now, we will calculate the height covered while covering these number of steps:

$Height\ Covered = H = (n)(Height\ for\ 1\ step)\\\\H = (0.2\ m/step)(650\ steps)\\H = 130\ m$

Now, we will calculate the amount of work done while covering this distance:

$Work = W = mgH = \\W = (60\ kg)(9.81\ m/s^2)(130\ m)$

<u>W = 76518 J = 76.518 KJ</u>

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A building made with a steel structure is 565 m high on a winter day when the temperature is 0◦F. How much taller is the buildin

anyanavicka [17]

To solve this problem we apply the thermodynamic equations of linear expansion in bodies.

Mathematically the change in the length of a body is subject to the mathematical expression

$\Delta L = L_0 \alpha \Delta T$

Where,

$L_0 =$ Initial Length

$\alpha =$ Thermal expansion coefficient

$\Delta T =$ Change in temperature

Since we have values in different units we proceed to transform the temperature to degrees Celsius so

$0\°F \Rightarrow (0-32)*\frac{5}{9} = -17.77\°C$

$103\°F \Rightarrow (103-32)*(\frac{5}{9})= 39.44\°C$

The coefficient of thermal expansion given is

$\alpha = 1.1*10^{-5}/\°C$

The initial length would be,

$L_0 = 565m$

Replacing we have to,

$\Delta L = L_0 \alpha \Delta T$

$\Delta L = (565)(1.1*10^{-5})(39.44-(-17.77))$

$\Delta L = (565)(1.1*10^{-5})(39.44-(-17.77))$

$\Delta L = 0.355m$

This means that the building will be 35.5cm taller

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2 years ago

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The answer is a because
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3 years ago

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Mass x height x gravity

4 0

3 years ago

A singly charged ion of 7Li (an isotope of lithium which lost only one electron) has a mass of 1.16 ×10^-26 kg. It is accelerate

MaRussiya [10]

Explanation:

It is given that,

Mass of lithium, $m=1.16\times 10^{-26}\ kg$

It is accelerated through a potential difference, V = 224 V

Uniform magnetic field, B = 0.724 T

Applying the conservation of energy as :

$\dfrac{1}{2}mv^2=qV$

$v=\sqrt{\dfrac{2qV}{m}}$

q is the charge on an electron

$v=\sqrt{\dfrac{2\times 1.6\times 10^{-19}\ C\times 224\ V}{1.16\times 10^{-26}\ kg}}$

v = 78608.58 m/s

$v=7.86\times 10^4\ m/s$

To find the radius of the ion's path in the magnetic field. The centripetal force is balanced by the magnetic force as :

$qvB=\dfrac{mv^2}{r}$

$r=\dfrac{mv}{qB}$

$r=\dfrac{1.16\times 10^{-26}\ kg\times 7.86\times 10^4\ m/s}{1.6\times 10^{-19}\ C\times 0.724\ T}$

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4 0

3 years ago

A skateboarder is skating back and forth on the halfpipe as seen below. As he skates his energy transforms from potential energy

egoroff_w [7]

Answer:

Friction and air resistance cause some of his kinetic energy to be “lost”. This makes him slow down.

Explanation:

The law of conservation of energy states that in absence of frictional forces, the mechanical energy of an object (given by the sum of its kinetic and potential energy) is conserved. In such a situation, the skateboarder would never stop his motion, because potential energy is continuously converted into kinetic energy and vice-versa, but the total energy remains the same so he would never stop.

In a real world, however, this is not true. In fact, in a real world some frictional force are present, in particular:

- friction: this force is due to the contact between the skateboard and the surface of the halfpipe, and its direction is always opposite to the motion of the skateboarder

- Air resistance: this force is due to the resistance opposed by the molecules of air that the skateboarder meets during his motion, and its direction is also opposite to the motion of the skateboarder

This two forces are said to be non-conservative forces, which means that they cause some of the mechanical energy of the skateboarder to be "lost", in the sense that it is dissipated as heat and it is no longer available for the skateboarder.

Therefore, the correct option is

Friction and air resistance cause some of his kinetic energy to be “lost”. This makes him slow down.

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3 years ago