A 1.4 kg book is lying on a 0.73 m-high table. You pick it up and place it on a
ID: 2026882 • Letter: A
Question
A 1.4 kg book is lying on a 0.73 m-high table. You pick it up and place it on a bookshelf 2.1 m above the floor.Part A
How much work does gravity do on the book?
ANSWER:
W1 =
Part B
How much work does your hand do on the book?
ANSWER:
W2 =
Problem 21
Part A
At what speed does a 1900 kg compact car have the same kinetic energy as a 1.7×104 kg truck going 25 km/hr?
ANSWER:
km/hr
Problem 22
Part A
A 62 g particle is moving to the left at 24 m/s. How much work must be done on the particle to cause it to move to the right at 33 m/s?
ANSWER
Explanation / Answer
W1 = -m*g*D = -1.4*9.81*(2.1-0.73) = -18.82 J W2 = -W1 = 18.82 J Problem 21 25 km/hr = 6.944 m/s E_kin_truck = (1/2) m v² = 0.5*1.7E4 * 6.944² = 409915 J E_kin_car = E_kin_truck = 409915 = 0.5*1900*v² 431.489 = v² v = sqrt(431.489) = 20.77 m/s = 74.78 km/hr Problem 22 E_kin_begin = 0.5*0.062*24² = 17.856 J E_kin_end = -0.5*0.062*33² = -33.759 J W = 17.856- -33.759 = 51.615 J
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