1 Match the Beginning of Each Sentence with the Correct Ending. Write out Each Complete

Homework L1 Under pressure

HELP

1 Match the beginning of each sentence with the correct ending. Write out each complete sentence.

Beginnings Endings

A A big elephant does not sink into 1 because it has a pointed end. the mud B A dart goes into a dartboard very 2 because this gives them a large easily surface so they will not pierce people's skin. C A clown on stilts makes a deeper 3 because this spreads the force mark on the ground than a clown and stops the pin from going into without stilts your thumb. D Children's Robin Hood sets have 4 because its feet have a large rubber stickers on the arrows area. E A drawing pin has a flat top 5 because the stilts have a very small surface area.

2 Some of the statements below are true and some are false. For each statement, write down ' true' or ' false'. a A nail will go into hard wood because the force of the hammer is concentrated at the point. b A duck does not sink into the mud at the edge of the pond because its pressure is spread over large webbed feet. c A fork goes into the soil more easily than a spade because the force from the person's foot is spread over a smaller area. d Ben and Bob weigh the same but Ben has bigger feet, so Ben will make deeper footprints on a sandy beach than Bob.

CORE

3 The surface areas of Animal Surface area of each foot in cm2 different animals' feet are given in the table on the A 9 right. The animals are B 1500 elephant, dog, guinea pig and polar bear. C 1 D 600

a i Animal B is an African elephant. Suggest why it is an advantage for an elephant to have such a large foot. ii What is the total surface area of all the elephant's feet? iii If the total force exerted by the elephant on the ground is 300 000 N, what is the total pressure on the ground from all four feet? Show how you reached your answer. b i Which animal might be a polar bear? ii Explain your reasoning.

EXTENSION

4 Joe weighs 75 N and has a mountain bike, which weighs 10 N. He usually pumps up the tyres quite hard. When it is very muddy he lets some air out of the tyres because he thinks this makes the bike easier to ride. The table shows the area of each tyre that is in contact with the ground.

State of the Area in contact with the ground (m2) tyre Normal 0.12 x 0.05

Deflated 0.13 x 0.07

In the calculations below, give your answers to the nearest whole number. a Calculate the pressure exerted by each tyre on the ground when Joe is riding his bike i when it is inflated normally ii when some air has been let out. b In which state will the tyres make the deepest marks in the ground? c Joe went on a diet and lost some weight. Calculate Joe's new weight, to the nearest Newton, if the pressure exerted by each tyre on the ground with both tyres fully inflated is 6650 N/m2.