Can someone please help with physics?

Question

Please help me out here, I'm really confused...all help is appreciated...the more people the more I understand so please help me out...

4. A small box is resting on a larger box sitting on a horizontal surface. When a horizontal force is applied to the larger box, both boxes accelerate together. The small box does not slip on the larger box.
a) Draw a Free body diagram of the small box during its acceleration.
***I'm really confused on what forces are acting on it since it's sitting on top of the larger box and the force is applied to the larger box only...what would the diagram look like?

b) What force causes the small box to accelerate horizontally
c) If the acceleration of the pair of boxes has a magnitude of 2.5 (meters/second)², determine the smallest coefficient of friction between the boxes that will prevent slippage. [final answer was given as 0.26]

5. Draw a Free body diagram for the larger box in question 4 when it's accelerating.

Answer 1

Here are the key things you need to know:

Forces acting on the small box:
- gravity attracting its mass (pulling it downward)
- large box (pushing it upward)
- friction force between the two boxes (pushing it forward)

Forces acting on the large box:
- gravity attracting its mass (pulling it downward)
- the weight of the small box (= the force of gravity on the small box) (pushing it downward)
- friction force between the two boxes (pushing it backward)
- friction force between the large box and the underlying surface (pushing it backward)
- the horizontal force (pushing it forward)

First, treat the two boxes as a single mass, resting on the surface and being accelerated by the horizontal force. Calculate the force of friction between the large box and the surface (remembering that the weight of both boxes is acting to push it against the underlying surface). Calculate the force needed to both overcome this friction and to accelerate the mass of the two boxes at the specified rate (the second part of this requires the formula F = ma). That is the horizontal force.

Now calculate the amount of force required to accelerate the small box at this rate. (Use F = ma again.) Divide this force by the weight of the small box to find the minimum coefficient of friction that will allow the large box to apply this force to the small box.

If you understand all this, you should be able to draw the two diagrams and answer the questions.
Good luck!

Answer 2

4. Assuming that air resistance is being neglected, the only force acting on the small box would its weight (mass * acceleration due to gravity). This force is acting downwards so it is negative.

5. The forces would be the applied force, weight(negative because it is acting downwards) and friction (opposes the motion of the box).

Answer 3

4. a) the small box and the big box have friction between each other.. in this case you must draw friction force favorable to the movement (it is the only force moving the small box)
b) the force of friction
c)
5. for the big one, only the force being applied and the friction with the ground must be drawn.. don't forget to consider the weight of the little one in calculating the friction with ground

Answer 4

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