Question

The work done by the frictional force on a pencil in drawing a complete circle of radius r=1/π meters on the surface by a pencil of negligible mass with a normal pressing force N=5N (u=0.5) is
a) +4J
b) -3J
c) -2J
d) -5J
please give me step be step solution

Answer 1

check the attachment

Answer 2

Answer:

The work done by the frictional force on a pencil in drawing a complete circle of radius r=1/π meters on the surface by a pencil of negligible mass with a normal pressing force N=5N (u=0.5) is = d) -5J

Explanation:

The work done by the frictional force on a pencil in drawing a complete circle of radius r=1/π meters on the surface by a pencil as in the question. So total distance travelled by the pencil is equal to the circumference of the circle drawn by the pencil.

Circumference of the circle = 2x π x (1/π) = 2

Normal pressing force on the pencil is N=5N (u=0.5)

Frictional force on the pencil = - μ N

=> 0.5 x 5

=> 2.5 N

∴ Workdone by the frictional force on a pencil = -2.5 x 2 = -5 J