Question

Exercise 19.
Repeat Exercise 3. with the contestant pulling the block of ice with a rope over his shoulder at the same angle above the horizontal as shown in Figure 5.7(b).

Answer 1

Exercise 19.

from a given figure :

"Pushing" is the best method of sliding a block of ice requires less force.

This is Exercise 3.

(a) the maximum frictional force in the knee joint of a person who supports 66.0 kg of her mass on that knee which is given as :

f_k = _k N                                { eq. 1 }

where, N = mg sin

inserting the value of 'N' in above eq.

f_k = _k (mg sin )                                     { eq.2 }

where, m = mass of the person = 66 kg

g = acceleration due to gravity = 9.8 m/s²

= making an angle above horizontal surface = 25 degree

_k = coefficient of kinetic friction of ice = 0.03

inserting all these values in above eq.2

f_{k (max)} = (0.03) (66 kg) (9.8 m/s²) sin 20⁰

f_{k (max)} = (19.404) (0.342)

f_{k (max)} = 6.63 N

(b) the maximum force of friction under such conditions is given as :

ten times greater than the weight being supported,

f_{k (max)} = 10 x mg sin                         { eq.3 }

inserting the values in eq.3

f_{k (max)} = 10 (66 kg) (9.8 m/s²) sin 20⁰

f_{k (max)} = 2212 N