Cheyanne Leigh
2020-10-25
Answered

A person jumps from a fourth-story window 15.0 m above a firefighter's safety net. The survivor stretches the net 1.0 m before coming to rest. (a) What was the average deceleration experienced by the survivor when slowed to rest by the net? (b)What would you do to make it "safer" (that is, generate a smaller deceleration): would you stiffen or loosen the net? Explain.

You can still ask an expert for help

Theodore Schwartz

Answered 2020-10-26
Author has **99** answers

First, we need to know how fast the person was falling when he hit the net. We know how far he fell, so it is a simple task of determining the his velocity:

$v={v}_{0}+at$

which means we need to know how long he was falling:

$d={v}_{0}+\frac{1}{2}a{t}^{2}$

I will assume is initial velocity was zero. We can then solve the above equation for t: (keep in mind d is the distance he fell,and a is gravity, both of these are negative quantities so the negatives cancel)

$t=\sqrt{\frac{2d}{a}}\approx 1.75\text{}s$

plugging t into the velocity equation:

$v=(-9.8)\left(1.75\right)\approx 17.15\text{}\frac{m}{s}$

Now the average deceleration can be found by taking the change in velocity over the change in time. But alas, we do not have tright off hand, so we need something else What we do know is that it took 1m to stop the person. Lets

which means we need to know how long he was falling:

I will assume is initial velocity was zero. We can then solve the above equation for t: (keep in mind d is the distance he fell,and a is gravity, both of these are negative quantities so the negatives cancel)

plugging t into the velocity equation:

Now the average deceleration can be found by taking the change in velocity over the change in time. But alas, we do not have tright off hand, so we need something else What we do know is that it took 1m to stop the person. Lets

Jeffrey Jordon

Answered 2021-10-06
Author has **2027** answers

Lets calculate speed just before hitting net

a) Person comes to rest in 1m

b)

for smaller a ,d have to be larger

so, loosen the net

asked 2021-02-19

An airplane propeller is 2.08 m in length (from tip to tip) and has a mass of 117 kg. When the airpline's engine is first started, it applies a constant torque of $1950\text{}N\cdot m$ to the propeller, which starts from rest.

a) What is the angular acceleration of the propeller? Model the propeller as a slender rod.

b) What is the propeller's angular speed after making 5.00 revolutions?

c) How much work is done by the engine during the first 5.00 revolutions?

e) What is the instantaneous power output of the motor at the instant that the propeller has turne through 5.00 revolutions?

a) What is the angular acceleration of the propeller? Model the propeller as a slender rod.

b) What is the propeller's angular speed after making 5.00 revolutions?

c) How much work is done by the engine during the first 5.00 revolutions?

e) What is the instantaneous power output of the motor at the instant that the propeller has turne through 5.00 revolutions?

asked 2021-04-25

A stunt man whose mass is 70 kg swings from the end ofa 4.0 m long rope along thearc of a vertical circle. Assuming that he starts from rest whenthe rope is horizontal, find the tensions in the rope that are required to make him follow his circular path at each of the following points.

(a) at the beginning of his motion N

(b) at a height of 1.5 m above the bottom of the circular arc N

(c) at the bottom of the arc N

(a) at the beginning of his motion N

(b) at a height of 1.5 m above the bottom of the circular arc N

(c) at the bottom of the arc N

asked 2021-01-10

A 730-N man stands in the middle of a frozen pond of radius 5.0 m. He is unable to get to the other side because of a lack of friction between his shoes and the ice. To overcome this difficulty, he throws his 1.2 kg physics textbook horizontally toward the north shore , at a speed of 5.0 m/s. How long does ittake him to reach the south shore?

asked 2020-12-05

A 5.00kg sack of flour is lifted vertically at a constant speed of 3.50m/s through a height of 15.0m. a) How great a force is required? b) How much work is done on the sack by the lifting force? What becomes of this work?

asked 2022-01-14

Two waves in one string are described by the wave functions:

${y}_{1}=\left(3.0cm\right)\mathrm{cos}(4.0x-1.6t)$

${y}_{2}=\left(4.0cm\right)\mathrm{sin}(5.0x-2.0t)$

where y and x are in centimeters and t is inseconds. Find the superposition of the waves$y}_{1}+{y}_{2$ at the points

x= 0.500, t=0.

where y and x are in centimeters and t is inseconds. Find the superposition of the waves

x= 0.500, t=0.

asked 2021-04-19

For the cellar of a new house a hole is dug in the ground, withvertical sides going down 2.40m. A concrete foundation wallis built all the way across the 9.6m width of the excavation. This foundation wall is 0.183m away from the front of the cellarhole. During a rainstorm, drainage from the streetfills up the space in front of the concrete wall, but not thecellar behind the wall. The water does not soak into the clays oil. Find the force the water causes on the foundation wall. For comparison, the weight of the water is given by:

$2.40m\cdot 9.60m\cdot 0.183m\cdot 1000k\frac{g}{{m}^{3}}\cdot 9.8\frac{m}{{s}^{2}}=41.3kN$

asked 2021-11-14

Let A and B be $$A=\left[\begin{array}{ccc}1& 0& -2\\ 3& 1& 0\\ 1& 0& -3\end{array}\right],\text{}B=\left[\begin{array}{ccc}1& 0& -3\\ 3& 1& 0\\ 1& 0& -2\end{array}\right]$$
Find an elementary matrix E such that EA=B.