A uniform beam weighing 1 N is used as a metre rule. The beam is supported by a pivot at the 30 cm mark. A 12 N weight is hung at the 0 cm mark and a 2 N weight is hung at the
60 cm mark as shown in Figure 5.19.
O cm
50 cm 60 cm
100 cm
수
► Figure 5.19
30 cm
mark 1 N
12 N
2 N
W
What is the weight W of a mass hung at the 100 cm mark in order to balance the beam?
Please help!

W =  4 N (to balance the beam)

Explanation:

take moment at support Δ

∑M at Δ = 0 (note: clockwise is + and counter clockwise is - )

0 = W(100 - 30) + 2(60-30) + 1(50-30) - 12(30)

0 = W70 + 2(30) + 1(20) - 360

0 = W70 + 60 + 20 - 360

0 = W70 - 280

280 = W70

W = 280 / 70

W = 4 N (to balance the beam)

to take the reaction at support Δ

Δ = 12 + 1 + 2 + 4

Δ = 19 N

proof that W = 4

∑M at 12N = 0

0 = 19(30) - 1(50) - 2(60) - W(100)

0 = 570 - 50 - 120 - 100W

100W = 400

W = 400 / 100

W = 4 N ok

answer: the rock sample is a sedimentary rock.

explanation:

it is given that:

mass of rock sample, m = 2.7 g

volume of rock sample,

so, density of rock sample will be

since, the density of rock sample is . hence, the rock sample is a sedimentary rock, whose densities varies between .

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.