2005 - JAMB Physics Past Questions and Answers - page 1

Marching soldiers crossing a suspension bridge are usually advised to break their steps to avoid damaging the bridge owing to resonance. The steps of the marching soldiers can set the bridge into vibration, and when the frequency of the bridge is equal to that of the steps of the soldiers, the resonance occurs,and at this resonance, the bridge vibrates violently with maximum amplitude, and can collapse.

The sharpness of the boundary of the shadow of an object is determined by the rays of light passing through the object. The smaller the rays passing through , that is from a point source, the more sharp the shadow becomes, but the more the rays, that is rays from a large source, the more blurred the shadow becomes.

the power of a lens is defined as the reciprocal of the focal length ,expressed in metre.Mathematically, the power of a lens in dioptres is given by:(100)/f(in cm).

thus for lens of power of 4.0 dioptres we have that: (100)/(f) = +4.0

f= (100)/(4.0) = 25cm

      = 0.25cm

for a real image 3 times the size of the object, it implies that the magnification 3 = v/u, 3 = 24/u, therefore 3u = 24, u = 8cm thus we have from the relation:m = (f)/(u)-f; that 3 = (f)/(8) - f. therefore f = 3(8-f) f = 24 - 3f ∴4f = 24; f = 6cm OR: (1)/(u) + (1)/(v) = (1)/(f).

(1)/(8) + (1)/(24) = (1)/(f)

therefore (3+1)/(24) = (1)/(f)

4/24=1/f;therefore 4f = 24

               f = 6cm

In a wheel and axle system of mechanic, the mechanical advantage is given by its ratio of the radius of the wheel R, to the radius of the axle r. that M.A = R/r

for a body projected at an angle θ to the horizontal, the time of the flight is given by T = (2u sin θ)/g =(2x 40)x sin (30)/10 =(2 x 40) x (0.5)/10 = 4.0secs.

In a purely capacity circuit, voltage lags behind current by 90°, or current leads voltage by 90°

Since 1/32, is the fraction left of any radioactive material after 5half lives, that is:

1/32= (1/2)⁵. Thus if a half life is 50 days, 5 half lives will be 50 x 5= 250 days

The force acting on moving charge in magnetic field is given by: F=q VBSin θ

sin θ =F=(8.0x10)^-14/1.6x10^-19x1.0x10⁶x1.0 = (8.0x10)¹⁴/16 x 10¹³

(8.0x 10)^-14/16x10^-14

=0.5000

∴ θ= sin^-1 0.5000

=30°