Emily challenges her friend David to catch a dollar bill as follows. She holds the bill vertically, with the center of the bill between David's index finger and thumb. David must catch the bill after Emily releases it without moving his hand downward. If his reaction time is 0.2 s, will he succeed? Explain your reasoning.


Answer 1


David will not  be able to catch the bill .


Reaction time = .2 s .

During this period bill will fall vertically between the fingers.

Distance of fall = 1/2 x g x t²

= .5 x 9.8 x 0.2²

= 19.6 cm or 20 cm .

Generally the bill has size of the order of 25 cm . From central point it requires a fall of 12.5 cm for the bill to escape the catch . Since fall is of 20 cm , that means bill will fall below the level of fingers in .2 s .

So David will not be able to catch the bill.

Related Questions


Define mechanics and describe its three major divisions


Mechanics is the branch of physics which deals with the study of motion of material objects.


There are three major division of mechanics





Calculate the speed of an electron (in m/s) after it accelerates from rest through a potential difference of 160 V.



v = 7.5*10⁶ m/s


While accelerating through a potential difference of 160 V, the electron undergoes a change in the electric potential energy, as follows:

ΔUe = q*ΔV = (-e)*ΔV = (-1.6*10⁻¹⁹ C) * 160 V = -2.56*10⁻¹⁷ J (1)

Due to the principle of conservation of energy, in absence  of non-conservative forces, this change in potential energy must be equal to the change in kinetic energy, ΔK:

ΔK = Kf -K₀

As the electron accelerates from rest, K₀ =0.

⇒ΔK =Kf = (2)

From (1) and (2):

ΔK = -ΔUe = 2.56*10⁻¹⁷ J =

where me = mass of the electron = 9.1*10⁻³¹ kg.

Solving for vf:

⇒ vf = 7.5*10⁶ m/s


describe how energy is transferred in a mechanical wave


A mechanical wave requires an initial energy input. Once this initial energy is added, the wave travels through the medium until all its energy is transferred. In contrast, electromagnetic waves require no medium, but can still travel through one

Which hypothetical scenario would result in the moon not having different phases?


If the moon didn't revolve around the earth it would not have phases but in fact it revolves around the earth. A full moon is when the sun is behind the earth and illuminating the moon.The different phases of the moon are proof that it revolves around the earth,

Disks A and B are identical and roll across a floor with equal speeds.Then disk A rolls up an incline, reaching a maximum height h, and disk B moves up an incline that is identical except that it is frictionless. Is the maximum height reached by disk B greater than, less than, or equal to h?



Greater than h


Since, Disks A and B are identical and roll across a floor with equal speed, they would start up on the incline with equal kinetic energies. Disk A reaches a maximum height of h. Disk B moves up the incline which is friction less.

Due to incline being friction less, there will be no dissipation of energy due to friction which would occur for Disk A as it rolls up the incline. Thus, Disk B would roll up to a height greater than h.


Which of the following statements is true about conductors and insulators? Select all that apply. conductors have few free electrons

conductors have many free electrons

insulators have few free electrons

insulators have many free electrons

conductors are ideal
for electrical wiring

insulators are ideal for electrical wiring


Conductors and insulators.

The insulators is a material that consists of a few electrons and they permit very little flow of electrical current. While the conductors are very good conductors of electricity. The metal is a very good conductor while rubber is a poor insulator.

Hence the answer is conductors possess free electrons, while insulators have few free electrons

  • The conductor has thus been used for wiring purposes and can be effectively used made to use energy; The insulator is poor absorbers and thus are unable to transfer energy.

Thus the options B, C, and E are correct.

Learn more about the following statements.

Conductors have many free electrons
insulators have few free electrons
conductors are ideal for electrical wiring

Which statement describes the daily motion of the moon? rises and sets at same time
rises and sets 50 minutes later
rises 50 minutes later, sets 50 minutes earlier
rises 50 minutes earlier, sets 40 minutes later


Rises and sets 50 minutes later. If somehow you are still on this question.


rises and sets 50 minutes later


ik its been years but its ok bahaha :>


Rosie went on a hiking trip. The first day she walked 181818 kilometers. Each day since, she walked 90\%90%90, percent of what she walked the day before. What is the total distance Rosie has traveled by the end of the 10^\text{th}10 th 10, start superscript, t, h, end superscript day? Round your final answer to the nearest kilometer.



117 km


The 1st day, Rosie walked

The 2nd day, she walked 90% of the distance walked the previous day, so

Similarly, on the 3rd day she walked

So the distance walked at the nth day is

This is a geometrical series of the form

where and . The sum of such a series is given by

So for n = 10, we find:

We will see that the total distance walked at the end of the 10 days is 117km

What is the total distance Rosie walked?

We know that on the first day, she walks a distance of 18 km.

The next day, she walks 90% of that, so the distance walked on day 2 is:

d(2) = (90%/100%)*18km = 0.9*18km

On day 3, she walks the 90% of what she walked on day 2, so the distance is:

d(3) = (90%/100%)*0.9*18km = 0.9^2*18km

We already can see tha pattern here, on day x, she walks a distance:

d(x) = 18km*(0.9)^(x - 1)

This is an exponential decay.

Then the total distance walked on the first 10 days is:

D = 18km*(1 + 0.9 + 0.9^2 + 0.9^3 + ... + 0.9^9) = 117 km

If you want to learn more about exponential decays, you can read:


The state of matter is an example of a physical property. Why is the state of matter considered aphysical property, even though a substance may change between a solid, liquid, and gas?


The three states of matter are the three distinct physical forms that matter can take in most environments: solid, liquid, and gas. In extreme environments, other states may be present, such as plasma, Bose-Einstein condensates, and neutron stars. Further states, such as quark-gluon plasmas, are also believed to be possible. Much of the atomic matter of the universe is hot plasma in the form of rarefied interstellar medium and dense stars.
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