Question

Plzz provide me an appropriate answer

Answer 1

see crossproduct is zero when angle between two vector whose cross product we are doing is zero as
a×b=absin(theta)
where there is angle between a and b vector so when theta=0 cross product is zero
now
Dr/dt is velocity
also
p =mv
so basically momentum is also a velocity vector multiply by mass
so direction of both is same
hence theta=0
hence the cross product

Answer 2

Explanation:

What is the work done by a force of 1gwt. in displacing a body of mass 5 gm through 1 cm. Take g=10m/s²