Two kids create a makeshift seesaw by setting a 4-m long uniform plank on a saw horse. the saw horse is 0.5 m to the left of the center of mass of the plank. the child of mass m1 = 42 kg sits at the left end of the plank. the child of mass m2 = 31 kg sits 1 m to the right of the center of mass of the plank. what is the mass of the plank?

The mass of the plank is 33 kg.

Explanation:

Given that,

Length of plank = 4 m

Distance in left from the center= 0.5 m

Mass of child = 42 kg

Mass of other child = 31 kg

Distance in right from the center= 1 m

We can sum torques around the saw horse; each force generates a torque equal to force x distance from saw horse

We need to calculate the torque for first child

Using formula of torque

Put the value into the formula

We need to calculate the torque for second child

The child is 1.5 m from the saw horse

Using formula of torque

Put the value into the formula

The weight of the plank produces a clockwise torque

We need to calculate the mass of the plank

Using balance equation of torque

Put the value into the formula

Hence, The mass of the plank is 33 kg.

think its the third option

wire in brush may conduct electricity from cell to drill and vice versa electrc shock possible