For an object thrown vertically upward, its time of flight is equal to the equation below:
t = 2v/g
where
t is the time of flight
v is the initial velocity
g is the acceleration due to gravity equal to 9.81 m/s²
Substituting the values,
7.07 = 2v/9.81
v = 34.68 m/s
Answer:
A) some of the rocks energy is transformed to thermal energy
Explanation:
If we neglect air resistance during the fall of the rock, than the mechanical energy of the rock (which is sum of its potential energy and its kinetic energy) would be constant during the entire motion, so the total energy of the rock at the top would be the same as the sum of its potential energy and kinetic energy at the bottom.
However, this not occurs, due to the presence of air resistance. In fact, air resistance acts against the fall of the rock, and because of the friction between the molecules of air and the surface of the rock, the rock loses part of its energy. This energy is converted into thermal energy of the molecules of the air.
Gravitational Potential Energy = weight x height
for 1 meter:
GPE = 5 x 1
= <u>5N</u>
for 1.5 metres:
GPE = 5 x 1.5
= <u>7.5N</u>
for 2 metres:
GPE = 5 x 2
= <u>10N</u>
I will assume here that the well is sufficiently short so that the time the sound takes to come from the bottom of the well to our ear is negligible.
Since the pebble moves by uniformly accelerated motion, the distance it covers is given by
where
is the gravitational acceleration
is the time the pebble takes to reach the bottom of the well
Therefore, the depth of the well is
and the correct answer is B.
If this metal is replaced with a metal having a higher work function, yellow light may be able to remove electrons but the electrons ejected will have less kinetic energy and the required stopping potential would be less. So in order to remove electrons( with more kinetic energy), we need to use light having even more shorter wavelength than yellow light because light with shorter wavelength possesses more energy and the electrons will eject with greater kinetic energy. Hence BLUE light should be used for better results cuz its wavelength is less than yellow light. Hope it helps.