Ask question

Ask question

All categories

2 years ago

13

A person bends over to grab a 20 kg object. The back muscle responsible for supporting his upper body weight and the object is l

ocated 2/3 of the way up his back (where it attaches to the spine) and makes an angle of 12 degrees with the spine. His upper body weighs 36 N. What is the tension in the back muscle?
A. 1500 N
B. 1700 N
C. 2700 N
D. 3500 N

1 answer:

ANTONII [103]2 years ago

4 0

Answer:

C) 2700 N

Explanation:

As per FBD of the given situation we can say that torque due to tension in the spine is counter balanced by the torque due to weight of upper part of the body and the weight of the object

The tension force is acting at an angle of 12 degree

while both weight are acting perpendicular to the length

so here we have

$\tau_{clockwise} = \tau_{counterclockwise}$

$m_1g(\frac{L}{2}) + m_2g(L) = Tsin12(\frac{2L}{3})$

now we have

$36(9.81)(\frac{L}{2}) + 20(9.81)(L) = T sin12(\frac{2L}{3})$

T = 2700 N

You might be interested in

True or false<br><br>energy can neither be created nor be destroyed<br>

muminat

Answer:

the correct answer is TRUE

Hope it helps you

have a nice day

4 0

2 years ago

Read 2 more answers

Why does physics involve math?

Scrat [10]

Physics involves math because calculations have to be made and u use math to make calculations

3 0

2 years ago

If 20 beats are produce with one second which of the following frequency could possibly be held by two sound waves traveling thr

musickatia [10]

ANY two frequencies whose difference is 20 Hz.

8 0

3 years ago

A 12.6-kg monkey is hanging by one arm from a branch and swinging on a vertical circle. As an approximation, assume a radial dis

Zinaida [17]

Answer:

a)27.3N

b)150.78N

Explanation:

Having in mind the conservation of energy, as the monkey goes up (gaining potential gravitational energy) the kinetic energy must be reduced, so reducing the velocity of the monkey. So the maximum velocity will be at this lower point with a velocity of 1.36m/s

From this velocity and the radius we can calculate the angular velocity for the monkey center of mass:

$w=\frac{1.36m/s}{0.853m} =1.594 /s$

with this we can calculate the centripetal force magnitude:

$F=m*w^{2} *r=12.6kg*(1.594/s)^{2} *0.853m=27.3N$

On the mokey center of mass we have two opposite forces acting, the tension of the arm and the weight, in order for the monkey to continue swinging the resolt of this two forces must be equal to the centripetal force:

$T-P=F=>T=F+P$

$T=27.3N+12.6kg*9.8m/s^{2}=150.78N$

8 0

2 years ago

What is the energy of a photon that has the same wavelength as an electron having a kinetic energy of 15 ev?

serg [7]

Answer: $6.268(10)^{-16}J$

Explanation:

The kinetic energy of an electron $K_{e}$ is given by the following equation:

$K_{e}=\frac{(p_{e})^{2} }{2m_{e}}$ (1)

Where:

$K_{e}=15eV=2.403^{-18}J=2.403^{-18}\frac{kgm^{2}}{s^{2}}$

$p_{e}$ is the momentum of the electron

$m_{e}=9.11(10)^{-31}kg$ is the mass of the electron

From (1) we can find $p_{e}$ :

$p_{e}=\sqrt{2K_{e}m_{e}}$ (2)

$p_{e}=\sqrt{2(2.403^{-18}J)(9.11(10)^{-31}kg)}$

$p_{e}=2.091(10)^{-24}\frac{kgm}{s}$ (3)

Now, in order to find the wavelength of the electron $\lambda_{e}$ with this given kinetic energy (hence momentum), we will use the De Broglie wavelength equation:

$\lambda_{e}=\frac{h}{p_{e}}$ (4)

Where:

$h=6.626(10)^{-34}J.s=6.626(10)^{-34}\frac{m^{2}kg}{s}$ is the Planck constant

So, we will use the value of $p_{e}$ found in (3) for equation (4):

$\lambda_{e}=\frac{6.626(10)^{-34}J.s}{2.091(10)^{-24}\frac{kgm}{s}}$

$\lambda_{e}=3.168(10)^{-10}m$ (5)

We are told the wavelength of the photon $\lambda_{p}$ is the same as the wavelength of the electron:

$\lambda_{e}=\lambda_{p}=3.168(10)^{-10}m$ (6)

Therefore we will use this wavelength to find the energy of the photon $E_{p}$ using the following equation:

$E_{p}=\frac{hc}{lambda_{p}}$ (7)

Where $c=3(10)^{8}m/s$ is the spped of light in vacuum

$E_{p}=\frac{(6.626(10)^{-34}J.s)(3(10)^{8}m/s)}{3.168(10)^{-10}m}$

Finally:

$E_{p}=6.268(10)^{-16}J$

4 0

3 years ago