I can not solve the problem if I do not have the mass.
Dont really understand what youre asking but switches can be used to turn things on and off.
Answer:
B. +5.75 m/s
Explanation:
When there are two bodies, a and b, whose velocities measured by a third observer (in this case, the ground) are
and
respectively, the relative velocity of B with respect to A is given by:

Thus, the velocity of the girl relative to the lawnmower is:
