Here are a couple of questions for all you physic whizzes.please answer and defend and support your answers!?

Question

1) A horizontal force is applied to a wooden box restin on a table top. As soon as the box begons to slide, the force of friction will (1) decrease (2) increase (3) remain the same

2) A constant unbalanced force od friction acts on a 15 kg mass mocing along a horizontal surface ti rest in 1.50 sec, what is the magnitude of the force of friction? (1) 10.0 N (2)100N (3) 147 N (4) 150 N

3) If a boat is moving along at constant speed it may be assumed that (1) a net force is pushing it foward (2) the sime of only vertical forces is zero (3) the buoyant force is greater than gravity (4) the sum of only horizontal forces is zero (5) the sum of all forces is zero

Answer 1

1) When an object is stopped, microscopic (or larger) hills and valleys on the two contacting surfaces tend to interlock - the hills on one surface poke into the valleys of the other surface. When a piece is sliding, the hills kind of bump each other; they never settle into the valleys. Sliding friction is always less than static friction.

2) In order to calculate the force of friction, you must know the initial velocity of the block. Knowing its mass and the time it takes to stop is insufficient to calculate the force required.

3) Vertical forces cause the boat to sink (or fly away). Horizontal forces cause the boat to speed up or slow down. If the boat is at constant speed, it is not sinking, not flying, not speeding up, not slowing down. The answer should be obvious.