1999 - JAMB Physics Past Questions and Answers - page 5


From Ohms Law, E = I(R +X)
=> E = I1(R1 + X)
again, E = I2(R2 + X)
=> I1(R1 + X) = I2(R2 + X)
∴ 5(8 + X) = 7(5 + X)
40 + 5X = 35 + 7X
7X - 5X = 40 - 35
2X = 5
X = 5/2
= 2.5Ω
Users' Answers & Comments
Energy stored in a capacitor is given by
E = 1/2CV2
But effective capacitance for the parallel arrangement is given by
C = C1 + C2
= 2 + 3
= 5μF = 5 x 10-6 x (100)2
∴E = 1/2CV2
= 1/2 x 5 x 10-6 x 104
2.9 x 10-2J
Users' Answers & Comments
Power = IV = I2R = V2/R
In terms of e.m.f E, of a cell we have
IE = I2R = E2/R
∴P1 = E2/R; P2 = E2/R2/E2/R2
= E2/R1 x R2/E2 = R2/R1
∴P1/P2 = R2/R1
Users' Answers & Comments
The effective V =
√ VR2 + VL2
=
√ 62 + 82
=
√ 36 + 64
=
√ 100
10V
Users' Answers & CommentsLet the forces be F1, and F2.
F1 = m1 a1 = 3 x 2 = 6N
F2 = m2 a2 = 1 x 9 = 9N
F1F2 = 69 = 23
Thus ratio of forces is 2: 3
Users' Answers & CommentsFrom principle of conservation of linear momentum,
(0.05 x 200) - (0.95 x 0) = (0.05 + 0.95) x V (since collision is inelastic).
Thus V = 10m/s.
K.E = 1/2 (0.05 + 0.95) x 102
K.E = 1/2 (1 x 100) = 50 J
Users' Answers & Comments(take g = 10ms-2)
Height h = 1/2 (U2/g) = 102/20 = 5m
Energy before hitting ground is = P.E at the height of 15m.
P.E = mgh = 0.1 x 10 x 15 = 15 J
Users' Answers & Comments