A 40-kg girl is running through the supermarket and jumps onto a stationary shopping cart full of groceries that has a total
mass of 80-kg. They roll away together at a speed of 7 m/s.
How fast must she have been running before the collision?
m/s

electrical potential energy =0.072 j

explanation:

electrical potential energy is given by

u= q δv

q= charge=6 c

δv= potential difference and is given by

δv= e d

e= electric field

d= distance=5 mm=0.005 m

δv=2.4 (0.005)=0.012 v

now electric potential energy= u= q δv

u=6 (0.012)

u=0.072 j