<span>Answer:
skater x km/h
cyclist 20 faster x + 20 km/h
skater 30 km
cyclist 80 km
skater time = cyclist time
t=d/r
30 / x = 80 /( x + 20
cross multiply
30 ( x + 20 ) = 80 x
30 x + 600 = 80 x
30 x - 80 x = -600
-50 x = -600
/ -50
x = 12 km/h
12 km/h skater</span>
Answer:
lithium
Explanation:
A lithium atom contains 3 protons in its nucleus irrespective of the number of neutrons or electrons. Notice that because the lithium atom always has 3 protons, the atomic number for lithium is always 3. The mass number, however, is 6 in the isotope with 3 neutrons, and 7 in the isotope with 4 neutrons.
Since energy cannot be created nor destroyed, the change in energy of the electron must be equal to the energy of the emitted photon.
The energy of the emitted photon is given by:

where
h is the Planck constant
f is the photon frequency
Substituting

, we find

This is the energy given to the emitted photon; it means this is also equal to the energy lost by the electron in the transition, so the variation of energy of the electron will have a negative sign (because the electron is losing energy by decaying from an excited state, with higher energy, to the ground state, with lower energy)
When the student the sled jumps off toward the north , the sled most likely move towards the south.
<h3>What is the Newton third law?</h3>
According to the Newton third law of motion, action and reaction are equal and opposite. This means that the direction of the reaction force must also be opposite to that of the action.
As such, when the student the sled jumps off toward the north , the sled most likely move towards the south.
Learn more about Newton third law:brainly.com/question/974124
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All wheelchairs may be secured
so that the user is facing the curb side of the vehicle is true. The answer is
letter A. It provides a unique 180 degree powered rotation which makes it
possible to raise, lower and rotate fully.