Answer:

Explanation:
Let say the empty wagon has mass "M"
now by newton's II Law we will have

now it is given that empty wagon is pulled with acceleration 1.4 m/s/s
now we will have

now a child of mass three times the mass of wagon is sitting on the empty wagon
so here we have


so we have

Answer:
(d) A strong electron-phonon interaction
Explanation:
Superconductivity -
The phenomenon of superconductivity is due to the attractive force between electrons from the exchange of the phonons that cause the bound pair of electrons known as cooper pairs .
A strong electron -phonon intercation is suitable condition for superconductivity and high resistance .
Y₀ = initial position of the balloon at the top of the building = 44 m
Y = final position of the balloon at halfway down the building = 44/2 = 22 m
a = acceleration of the balloon = - 9.8 m/s²
v₀ = initial velocity of the balloon = 0 m/s
v = final velocity of the balloon = ?
using the kinematics equation
v² = v₀² + 2 a (Y - Y₀)
inserting the values
v² = 0² + 2 (- 9.8) (22 - 44)
v = 20.78 m/s