Answer:
Density=mass/volume 40 divided by 8 =5
Out of all the options, only body massager which uses electric energy to move back and forth is using motor here. It is because a motor converts electrical energy to Mechanical energy and only massager obeys it among all the options.
In short, Your Answer would be Option C
Hope this helps!
Answer : The force will be 4501.9
We can see that, two forces acting on the dummy in two different direction.
We know that, here two forces are given in perpendicular direction with each other.
We know the force is the vector addition law so, we will use the Pythagoras theorem for the resultant of the vectors
Now, the net force is

Two forces is given,


Now, the net force is



Hence, the force will 4501.9 N
As we said to the two people name A and the single person nameB.as every person make an acceleration 60ms2.so group A has more acceleration then group B. because in A there are two person so we add 60+60=120ms2. so group A can produce 120ms2 while groupB can produce 60ms2. i hope it will help you.