Bisa dibantu mengerjakan dengan caranya?

3.
I = Σ(m.r^2) = 2.(1^2) + 4(1^2) + 1(3^2)
I = 2 + 4 + 9 = 15 kg.m^2

4.
Usaha (W) = Q1 - Q2
Cari dl Q2

Q2/Q1 = T2/T1
Q2/ 1500 = 500/750
Q2 = 750000 / 750
Q2 = 1000 Joule

Jadi
W = Q1 - Q2
W = 1500 - 1000
W = 500 Joule