Due to your excitement over getting to do some more physics homework before spri

Question

Due to your excitement over getting to do some more physics homework before spring break, you throw your physics book into the air. For the following questions, assume all motion takes place solely in the y-direction, with up defined as the positive direction. The book (m = 1.5 kg) leaves your hands with a velocity of 8 m/s straight up. What is the impulse of the net force on the book while it is in the air (assumed to be free-fall) from the time you release it, to the instant just before it is back in your hands at the same height? Use impulse to determine the time the book is in the air. In order to throw the book into the air, you moved your arm vertically through a distance of 0.3 m. Use the principle of work to determine the average force you exerted on the book over this distance. Now, use the principle of impulse to determine how long the book was in your hands while throwing it.

Explanation / Answer

a) impulse = m*(delta v) = 1.5*2*8 = 24

b) F*(T) = 24

=> T = 24/(1.5*9.8) = 1.632 sec

c) F = (0.5*1.5*8*8 + 1.5*9.8*0.3)/0.3 = 174.7 N

d) t = sqrt(2*0.3/9.8) = 0.247 sec

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