Plz help on these 2 physics problems?

Question

Plz help on these 2 physics problems?
1. The top pulley hanging from the support produces only a change in direction of the effort force and not any mechanical advantage. Explain.

2. Determine the relationship between the number of strands supporting a block and tackle and its mechanical advantage.

note that...
mechanical advantage=Resistance(load)N/Effort(force)...
which is usually>1

Answer 1

If you place a pulley on the ceiling, place a rope through it to lift a load on the floor and pull on the rope, there is no mechanical advantage. That is because for every inch you move the rope, the load moves an equal inch. Draw a free body diagram for the load. The tension in the single rope is the same as the weight of the load, which is what you have to pull (change in direction) to lift it.

If you have a load lifted by a block and tackle system, draw a free body diagram and if there are more than one rope, say 4 ropes, the force in each rope would be 1/4 of the load, thus you have a mechanical advantage = 4, but you have to pull 4 times the length of rope.

Answer 2

1 a) I agree with the previous answer 1 b) This one is interesting, and can probably be debated. The previous answer is true: for a given amount of water evaporated, the heat transfer will be less. But what if our body could produce more sweat? Being the evaporation process faster, it would be possible that the heat transfer would be faster, resulting in a more effective cooling (but honestly, I'm not sure on this one). 2) With fresh water sprayed, the ambient temperature has to be below zero for long enough to transfer enough energy away from the water to turn it into ice, therefore it delays the decrease in temperature, making it stay at a 0 degrees plateau for a while (while changing phases from liquid to solid).