Answer:
If the system consists of the block only, the work done by the gravity is negative.
If the system consists of the block and the earth the work done by the gravity is zero.
Explanation:
If the system consists of the block only, then the system experiences two external forces: one exerted by the hand that lifts the block vertically upward and other exerted by the earth (gravity), which is opposed to the movement of the system, so the work done by gravity is negative.
On the other hand, if the system consists of the block and the earth, then only exists a external force which is the exerted by the hand. So, the force exerted by gravity is zero.
The momentum of the
x-ray photon is p = h/lambda . Lambda is the wavelength (0.30nm=3x10^(-9)m) and
h is Planck's constant,(h=6.62607004 × 10-34<span> m2 kg / s).The
momentum is: 2.2 x 10^(-25).</span>
The momentum can be calculated
also as: p=mv, where m is the mass of the electron and v is the speed.
So v=p/m,p is known,and
also the mass of the electron (m=9.10938356 × 10-31<span> kilograms).</span>
v=2.2 x 10^(-25)/9.10938356
× 10-31<span> kilograms=0.24 x 10^6 m/s</span>
Answer: silicon,or maybe none.
Explanation: I searched it up not really sure sorry
(6) first choice: the frequency appears higher and wavelength is shorter.
The car approaches a stationary observer and so the sound will appear to have shorter wavelength. This creates an effect of its siren to sound with higher frequency than it would do if both were stationary.
(7) The Doppler formula for frequency in the case of a stationary observer and source approaching it is as follows:

The wavelength is then

The third choice "0.80m; 431Hz" is correct