# A woman is celebrating her 29th birthday. How old is she?

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A woman is celebrating her 29th birthday. How old is she?
BRAIN TEASER A woman is celebrating her 29th birthday. How old is she?

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

QUESTION 1 You’re helping to bring the garbage bins to the curb for garbage pick-up. You push the bin with a constant force of magnitude 35 N along your 21 m long driveway. How much work have you done? (Assume the effects of friction are negligible)

QUESTION 2 Page 128, #5 A store clerk moved a 4.4 kg box of soap without acceleration along a shelf by pushing it with a horizontal force of magnitude 8.1 N. If the employee did 5.9 J of work on the box, how far did the box move?

QUESTION 3 A snowboarder has just finished a run and is sliding to a stop at the bottom of the hill on the horizontal. She has a total mass of 63 kg and it takes her 15 m to come to a complete stop. The coefficient of kinetic friction between the snow and her board is 0.11. a) Draw a FBD of the snowboarder when she is moving along the horizontal surface. b) What is the magnitude of the kinetic friction acting on the snowboarder? c) Determine the work done by the kinetic friction.

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

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