BRAIN TEASERBRAIN TEASER

A woman is celebrating her A woman is celebrating her 2929thth birthday. How old is she? birthday. How old is she?

SOLUTIONSOLUTION

On her 29On her 29thth birthday she is only 28 years birthday she is only 28 years old, that is, she has lived 28 full years. On old, that is, she has lived 28 full years. On your first birthday you had just been born, your first birthday you had just been born, and it was only on your second birthday and it was only on your second birthday that you reached the age of one year. that you reached the age of one year. Therefore, using the term “birthday” to Therefore, using the term “birthday” to describe one’s age is misleading. describe one’s age is misleading.

QUESTION 1QUESTION 1

You’re helping to bring the garbage You’re helping to bring the garbage bins to the curb for garbage pick-up. bins to the curb for garbage pick-up. You push the bin with a constant You push the bin with a constant force of magnitude 35 N along your force of magnitude 35 N along your 21 m long driveway. How much work 21 m long driveway. How much work have you done? have you done? (Assume the effects of friction are negligible)(Assume the effects of friction are negligible)

QUESTION 2QUESTION 2

Page 128, #5Page 128, #5

A store clerk moved a 4.4 kg box of A store clerk moved a 4.4 kg box of soap without acceleration along a soap without acceleration along a shelf by pushing it with a horizontal shelf by pushing it with a horizontal force of magnitude 8.1 N. If the force of magnitude 8.1 N. If the employee did 5.9 J of work on the employee did 5.9 J of work on the box, how far did the box move?box, how far did the box move?

QUESTION 3QUESTION 3A snowboarder has just finished a run and is A snowboarder has just finished a run and is sliding to a stop at the bottom of the hill on sliding to a stop at the bottom of the hill on the horizontal. She has a total mass of 63 kg the horizontal. She has a total mass of 63 kg and it takes her 15 m to come to a complete and it takes her 15 m to come to a complete stop. The coefficient of kinetic friction stop. The coefficient of kinetic friction between the snow and her board is 0.11. between the snow and her board is 0.11. a) a) Draw a FBD of the snowboarder when Draw a FBD of the snowboarder when

she is moving along the horizontal she is moving along the horizontal surface.surface.b)b) What is the magnitude of the kinetic What is the magnitude of the kinetic friction acting on the snowboarder?friction acting on the snowboarder?c)c) Determine the work done by the kinetic Determine the work done by the kinetic

friction. friction.

QUESTION 4QUESTION 4Page 129, #8Page 129, #8A student pushes a 0.85 kg textbook across a A student pushes a 0.85 kg textbook across a cafeteria table toward a friend. As soon as cafeteria table toward a friend. As soon as the student withdraws the hand (the force is the student withdraws the hand (the force is removed), the book starts slowing down, removed), the book starts slowing down, coming to a stop after moving 65 cm coming to a stop after moving 65 cm horizontally. The coefficient of kinetic friction horizontally. The coefficient of kinetic friction between the surfaces in contact is 0.38.between the surfaces in contact is 0.38.a)a) Draw a FBD of Draw a FBD of the book as it slows the book as it slows down, and calculate the magnitude of all down, and calculate the magnitude of all the forces in the diagram.the forces in the diagram.b)b) Calculate the work done on the book by Calculate the work done on the book by

the friction of the table.the friction of the table.