Gravity Work: Lifting 10N Book 1m at 0.5m/s

AI Thread Summary
When lifting a 10N book 1m at a constant velocity of 0.5m/s, the work done by gravity is questioned. The work done by the person lifting the book is 10J, but gravity's role is debated. Since the book is moving upward while gravity acts downward, it does not perform work on the book during this motion because there is no displacement in the direction of the gravitational force. The consensus is that gravity does not do work in this scenario, as work requires movement in the direction of the force. Therefore, the work done by gravity is zero.
Oxygen206
Messages
1
Reaction score
0

Homework Statement


The problem asks, "You lift a 10N book up in the air a distance of 1m at a constant velocity of 0.5m/s. The work done by gravity is:

a. -10J
b.-5J
c. zero
d. 5J
e. 10J


Homework Equations


W=FD
Wg=mgh


The Attempt at a Solution


So, the work done by whoever is lifting the book is 10J (W=FD) but with the hand still holding the book, is gravity doing work? I just really can't decide if gravity is doing "work" in this situation. Can someone point me in the right direction? Thank you!
 
Physics news on Phys.org
Oxygen206 said:
but with the hand still holding the book, is gravity doing work? I just really can't decide if gravity is doing "work" in this situation. Can someone point me in the right direction? Thank you!

The definition of work involves a distance as you pointed out. If the book is on the ground, does the gravity do work? As it is not moving, no.
By the way the definition of work can be found there : https://www.physicsforums.com/library.php?do=view_item&itemid=75. It's a line integral.
 
I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
Thread 'Collision of a bullet on a rod-string system: query'
In this question, I have a question. I am NOT trying to solve it, but it is just a conceptual question. Consider the point on the rod, which connects the string and the rod. My question: just before and after the collision, is ANGULAR momentum CONSERVED about this point? Lets call the point which connects the string and rod as P. Why am I asking this? : it is clear from the scenario that the point of concern, which connects the string and the rod, moves in a circular path due to the string...
Thread 'A cylinder connected to a hanging mass'
Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
Back
Top