Determine the direction of frictional forces (left, right, up down) for the objects:

1) A cup resting on top of a car. The car is moving and accelerating to the right.

2) A block being pushed to the right up an incline.

3)A block being placed at the middle of an incline (slope increasing to the right).

4)A cup sliding left across a table top

5) A book being pressed (force from the left) against a wall. The book is stationary.

friction is in opposite direction to motion, or opposite direction to a force which is tending to motion. For instance, on 3), friction is up the incline, to the right. 5) friction is upward, as gravity trying to make downward motion exists.

To determine the direction of frictional forces for the given scenarios, we need to consider the relative motion and the nature of the surfaces involved.

1) A cup resting on top of a car: When the car moves and accelerates to the right, the cup is also pushed towards the right by the car's motion. In this case, the frictional force will act towards the left, opposing the cup's tendency to slide off the car.

2) A block being pushed to the right up an incline: The block is being pushed to the right, and since it is on an incline, the block tends to slide downwards due to gravity. The frictional force will act up the incline to oppose the block's tendency to slide down.

3) A block being placed at the middle of an incline: In this case, the block is not being pushed or pulled, but simply placed at the middle of the incline. The only force acting on the block is gravity, which pulls it downward. Therefore, the frictional force will act up the incline to oppose the block's tendency to slide down.

4) A cup sliding left across a tabletop: When the cup slides left across the table, the frictional force will act towards the right, opposing the cup's motion and trying to prevent it from sliding further.

5) A book being pressed against a wall: The force is being applied to the book from the left, while the book is stationary against the wall. In this case, the frictional force will act towards the right, opposing the force applied to the book and preventing it from sliding or moving to the left.

To summarize:
1) Frictional force acts towards the left.
2) Frictional force acts up the incline.
3) Frictional force acts up the incline.
4) Frictional force acts towards the right.
5) Frictional force acts towards the right.