Answer:
Option C
100 J
Explanation:
Kinetic energy, KE is given by
where m is the mass and v is the velocity
Substituting 50 Kg for mass, m and 2 m/s for velocity v then we obtain

Therefore, the child's kinetic energy is equivalent to 100 J
'Pressure' is (force) / (area).
The only choice with those units is #1 .
Ok so here is the thing. It is necessary to introduce the atomic number Z into the following equation and the reason for that is that we are not working here with hydrogen (H). It will go like this:
<span>E=(2.18×10^-18 J)(Z^2 )|1/(ni^2 )-1/(nf^2 )| </span>
<span>E=(2.18×10^-18 J)(2^2 )|1/(6 ^2 )-1/(4 ^2 )|=3.02798×10^-19 J </span>
<span>After that we need to plug the E value calculated into the equation. Remember that the wavelength is always positive:</span>
<span>E=hc/λ 3.02798×10^-19 J=hc/λ λ=6.56×10^-7 m </span>
so 6.56×10^-7 m or better written 656 nm is in the visible spectrum
The centripetal acceleration is given by

where v is the tangential speed and r the radius of the circular orbit.
For the car in this problem,

and r=40 m, so we can re-arrange the previous equation to find the velocity of the car:
<span>500 km x (1 hr/88 km) = 5.68 hrs</span>