7. As a mass tied to the end of a string swings from its highest point...

7. As a mass tied to the end of a string swings from its highest point down to its lowest point, it is acted on by three forces: gravity, tension, and air resistance. Which force does (a) positive work? (b) negative work? (c) zero work?

Expert Solution

the mas is moving from its highest point down to its lowest point, which is tied to the end of a string and swinging

here the forces acting on the mass are , Tesnion and force of gravity and the air resistance which opposes the motion of the mass

as the mass moving form highest point to the lowest due to the force (component of the force of gravity ) acts towards the mean position and the displacement of the mass is also in the same direction so by definition of work done

W = F*S = F*S cos theta , theta is zero so W is +ve

the work done by the force of gravity is +ve

the work done by the tension force is , the tension force is perpendicular to the displacement of the mass

W = F*S cos theta = F*S cos90 = 0 J

so zero work will be done by the tension force

Now the work done by the air resistance is

as the air resistance acts in opposite direction to the displacement of the mass that is

W = F*S cos theta

W = F*S cos 180 = -F*S shows the -ve work done

(a) positive work by Gravity

(b) negative work by air resistance

(c) zero work by Tension

genius_generous answered 2 months ago

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