The rate at which work is done is called a. efficiency c. force b. effort time d. power

can be answered using momentum.

momentum = p

p1= mass1 * velocity1

p1 = p2

therefore

p1 = 6kg * 4m/s

p1 = 24kgm/s

p2=m2 * v2

24 kgm/s = 7kg * v2

v2 = 24 kgm/s / 7kg

v2= 3.42 m/s

force required to detach it is given by

charges are taken to be fundamental charge

now we have

so above is the minimum distance at which it will detach