The answer is B.
She can measure the mass of the water, marble and the graduated cylinder with the balance.
The volume of the water can be shown on the marked graduated cylinder, the volume of the marble can be measured by the volume difference of the water before and after the marble is put in.
Space is more hostile to the human body.
The correct answer is
<span>c. one person exerts more force than the other so that the forces are unbalanced.
In fact, the door is initially at rest. In order to move the door, a net force different from zero should be applied, according to Newton's second law:
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<span>where the term on the left is the resultant of the forces acting on the door, m is the door mass and a its acceleration.
In order to move the door, the acceleration must be different from zero. But this means that the resultant of the forces acting on it must be different from zero: this is possible only if the forces applied by the two persons are unbalanced, i.e. one person exerts more force than the other.</span>
Velocity increases with speed