Answer questions (1,2,4,8) gravity is 9.8

QUESTIONS ON CHAPTER THREE (Take the force of gravity as 9.8 N/kg.) *1. A man has a mass of 100 kg. Calculate the pressure he exerts on the ground in N/m when he is wearing (a) shoes, each shoe having an area of 200 cm2 in contact with the ground, (b) ice skating boots, each skate having a width of 0.25 cm and a length in contact with the ice of 4 cm, (c) skis, each of length 3 m and breadth 10 cm. 2. (a) An elephant of mass 6000 kg has four feet each of which may be considered as having a circular base of area 600 cm2 Calculate the average pressure exerted by each foot on the ground, if the elephant's weight is equally distributed among its feet. (b) A girl of mass 50 kg is wearing stiletto-heeled shoes. The soles of her shoes each have an area of 40 cm and the heels have circular tips of area 0.5 cm2. Calculate the pressure she exerts on the ground (i) when her weight is evenly distributed on both feet and (ii) when she is standing on her heels alone. Are stiletto heels or elephant's feet more likely to damage wooden floors? 3. Explain why: (a) a knife with a sharp blade is more easily able to cut through substances than one with a blunt blade, (b) nails have sharp points, (c) if two boys of equal mass slide down a snow-covered hill, one on a toboggan and the other on a metal tray, the toboggan runners leave a deeper impression in the snow than does the tray. 4. A drawing pin has a point of area 10-4 cm and is being pushed into a piece of soft wood. If a force of 50 N is exerted on the head of the pin, what is the pressure exerted by the point on the wood? If the same pressure must be exerted by the point of a nail (area 2 X 10-3 cm?) before it will begin to penetrate the wood, what force must be exerted on the head of the nail?8. A hovercraft has a mass of about 600 kg and a base area which may be taken as a rectangle of dimensions 10 X 8 m. When it is hovering it must exert a total downward thrust equal to its weight, this thrust being distributed over its base area. Calculate the average pressure exerted by the craft on the ground when hovering