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# True and false questions about mass and acceleration.

A small box of mass m is stacked on top of a large box of mass 3m. The interaction between the large box and the horizontal surface on which it slides is frictionless, but the interaction between the two boxes is NOT frictionless. The small box does not slide when a horizontal force F is applied to the large box. Which statements about the boxes are true?

A) The net force on box 3m is 3/4 F

B) The force that causes the acceleration of box m is friction

C) The acceleration of both boxes is the same

D) If the force stops acting, the boxes will slow down

E) The velocity of both boxes will be constant and non-zero

#### Solution Preview

We use Newton's second Law to the large box to evaluate statement (A):
<br><br>
<br><br>total force on large box = mass of large box * acceleration of large box;
<br><br>total force on large box = 3m * a, call this equation (1)
<br><br>
<br><br>we then solve for "a" as follows:
<br><br>
<br><br>"a" is not only the acceleration of the large box, but is also the acceleration of the system of both boxes so applying Newton's ...

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