General Knowledge - Physics - Discussion

Let's consider the comments of both vivek & rajal here.

1) when the body is supposed to lift upwards the gravity acts on it in the opposite direction (downwards).

2) when its rolled on an inclined surface the acts frictional force. But the work done is more in lifting upwards this is because for our consideration let it be mass=1kg,then weight=9.8N(w=m*g)

Then you need a force greater than the weight.But when its to move inclined instead of vertical less force is needed.

Let us consider its inclined at an angle of 1o degree then the body exerts a vertical force of (9.8*sin10)N and horizontal force of (9.8*cos10)N .

Now compare the case 1 & case 2 this shows that a body can be moved in (horizontal & inclined) easily than vertically.

[Note :to get the horizontal & vertical components refer parallelogram law]

Thank you a lot for reading my comment.

Whether you lift the stone or roll it up the slope ,stone gains potential energy equal to mgh .The stone gained this energy and by same amount you lost it ! Frictional force at the time of rolling up makes you to loose a little more of energy. You would have lost energy mgh when you lift it and mgh+ when you roll it up . Is it not better to lift then to roll it? Catch is here. There is mechanical advantage when you roll. Lever principle can be applied . Let the slope be 1/10. Rolling distance is 10 units whereas the lifting distance remains 1 unit . The effort is 1/10 now. You have a convenient comfort level ! In an ideal condition work done is same in both the cases. Rate of energy spending is less because you travel more distance. You spent less effort 1/10 and travelled 10 times more distance. Answer C is correct.

The work is the same. Assuming initial velocity is equal to a final velocity in both situations (that is, they all are zero), then neither experienced a change in kinetic energy. I am assuming that they both are moved to the same height because this would be totally illogical and uninteresting, as well as unsolvable if they were not. Therefore work done by gravity in both is mg, they both are moved same distance vertically and gravity is opposing them the entire time, therefore, equal and opposite work had to be done. Now, considering friction, it's totally irrelevant. The stone is rolled, therefore friction is not doing work of any kind it is simply providing the torque necessary to cause the angular velocity to remain constant.

At the bottom the energy of the stone is X.

At the top X+m.g.h (m= stone mass, g= gravitational force m, h= height of the hill).

So for the stone, it doesn't matter how it is brought up. Somebody must "add" that potential energy to the stone.

What must a stone carrier overcome? By rolling, the friction of the stone and the hill and the constant lifting of (part) of the stone weight to make it roll. He must add the potential energy and overcome the friction.

By lifting and walking the carrier must add all the potential energy the stone gained at the top, But no friction is involved.

So how D is the right answer?

We all know that work done in lifting a stone vertically upward or rising a heavy object is never less than or equal to when pulled or pushed using a ramp or inclined plane why? Because when lifting it upward work is done against gravity while when using ramp.

Some of the force applied to push the stone overcome friction while the other force remaining is used to overcome the load but in the absence of friction the work done in raising the stone is equal to the work done using the inclined plane to pull the stone. Thanks for reading.

The answer should be "C". The total work done is how much distance the stone was moved from it's initial position. When you lift you the stone up and bring it down to the final destination the total distance is same and so the work done is same. The time it takes you to roll it is generally longer than lifting it. So the work done is same but the rate of work done is different. You use more "power" in lifting it but same "energy" as rolling it up. So more power is used for lifting it than rolling it but same work (energy) is used.

Since the perpendicular distance between stone and earth is less than slope. Hence force between stone and earth through the path of the slope is less than that between same through the perpendicular path by universal gravitational law. And the distance is more for slope and less for perpendicular for the same case. So, energy is constant ie, mgh. The coefficient of friction makes us easy to roll and increases power. I think C is correct.

When we are lifting any object vertically, we just work against gravity (non-contact force). It is no matter whether the road is slope down or slope up. But in 2nd case, the concept of frictional force (contact force) is introduced. A roller touches its minimum parts on ground, so there less friction arises and it is easy to move. In case of moving downward we have to apply less energy than to moving upward just because of gravity.

When a stone is rolled up in an inclined plane than it is easier to apply force in upward direction because pulling is easier than pushing & one can use it's own weight while pushing as in case of pulley. So the answer will be D because firstly gravity is acting directly & vertically downward and secondly frictional force is introduced less in an inclined plane due to minimum contact with the road.

The work done in rolling is mg sin(theta) multiply by the length of the slope (assuming no friction) where theta is less than 90°. But work done in lifting vertically should be mgh where h is the height of the slope and angle to horizontal is 90. since sine of any angle less than 90° is always less than one, working in rolling is always less than the work done in lifting.