physics_ch7homework

physics_ch7homework - Chapter 7 Homework 1. In one day, a...

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Chapter 7 Homework 1. In one day, a 75-kg mountain climber ascends from the 1500-m level on a vertical cliff to the top at 2400 m. The next day, she descends from the top to the base of the cliff, which is at an elevation of 1350 m. What is her change in gravitational potential energy (a) on the first day = ( - ) ∆PE mg y2 y1 = . - 75 kg9 8 ms22400 m 1500 m = . × 6 62 105 J (b) on the second day? ∆PE = . - 75 kg9 8 ms21350 m 2400 m =- . × 7 72 105 J 2. A 5.00-kg sack of flour is lifted vertically at a constant speed of 3.50 m/s through a height of 15.0 m. (a) How great a force is required? = w mg = . . 5 00 kg9 8 ms2 = 49 N (b) How much work is done on the sack by the lifting force? What becomes of this work? = W Fs =( )( . ) 49 N 15 0 m = 735 J 3. A 120-kg mail bag hangs by a vertical rope 3.5 m long. A postal worker then displaces the bag to a position 2.0 m sideways from its original position, always keeping the rope taut.
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physics_ch7homework - Chapter 7 Homework 1. In one day, a...

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