At the local playground, a 16-kg child sits on the end of a horizontal teeter-totter, 1.5 m from the pivot point. On the other side of the pivot an adult pushes straight down on the teeter-totter with a force of 95 N. In which direction does the teeter-totter rotate if the adult applies the force at a distance of (a) 3.0 m, (b) 2.5 m, or (c) 2.0 m from the pivot

Explanation:

a ) the weight of child creates a torque equal to = mg x L where m is mass of the child , L is distance from pivot

= 16 x 9.8 x 1.5

= 235.2 Nm

force applied by man  F = 95 N , distance from pivot = 3 m

torque = force x distance from pivot

95 x 3 = 285 Nm which is greater than the torque produced by child so

teeter-totter will tilt towards adult person

b ) in this case distance of force from pivot = 2.5

torque produced by it

= 95 x 2.5

= 237.5 Nm , this too is more . So this time too,  teeter-totter will tilt towards adult person

c ) in this case distance of force from pivot = 2.0

torque produced by it

= 95 x 2.0

= 190 Nm

which is less than the torque produced by child so

teeter-totter will tilt towards child .  

and 1and 1

b. lifting dumbbell weight at 20-degree angle from the body after a 45-degree angle