Bill and Alice have just finished their shopping on the third floor of the local
ID: 1359490 • Letter: B
Question
Bill and Alice have just finished their shopping on the third floor of the local department store. Bill bought a fragile vase for his mother's birthday and is carrying it in a shopping bag. Bill and Alice take the elevator down to the ground floor. Let's examine the time interval during which the elevator is moving downward with a constant speed. Is the change in gravitational potential energy of the shopping bag in Bill's hand positive, negative, or zero? Explain your answer. Is the work done on the bag by Bill positive, negative. or zero? Explain.Explanation / Answer
Zero. Since he is going downward with constant speed the acceleration will be zero.
a=dv/dt=0.
Gravitational potential Energy=mgh
Since g=0,Gravitational potential Energy=0
If the lift is moving upward g will be negative. Since it doing a work against the gravitational potential energy.
Work done on the body is zero. Work done=F*distance
Force=mass*acceleration.
a=0,since it is moving with constant speed. So force=0
Work done =0
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