A graduated plank of length 90cm sits on a knife edge at 40cm mark. When a load of 50g is placed at 20cm, find the mass that will balance the plank at 70cm length.

33.3 g ≈ 33 g

Explanation:

Please see attached photo for explanation.

From the attached photo, M is the mass that we must obtain to balance the plank.

The mass, M can be obtained as follow:

Anticlockwise moment = clockwise moment

Anticlockwise moment = 50 x 20

Clockwise moment = M x 30

Anticlockwise moment = clockwise moment

50 x 20 = M x 30

Divide both side by 30

M = (50 x 20)/30

M = 33.3 g ≈ 33 g

Therefore, the mass that will balanced the plank at the 70 cm length is appropriately 33 g

the total distance that martina travels that day is

(distance from home to mom's office) plus (distance from mom's office to school)

plus (distance from school to library) plus (distance from library to friend's house)

plus (distance from friend's house to martina's house).

(we don't know what any of these distance actually is.)

god i hope this !