Physics Questions and Answers

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.

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.

Pressure = Force / Area = Weight of the man / Area of his feet
=> 2.8 x 10³ = Weight of the man / 4 x 10^-2
∴ Weight of the man = 2.8 x 10³ x 4 x 10^-2
= 112N

No explanation has been provided for this answer.

Safety gap = expansion of the rod

= \(\alpha \times L_0 \times \Delta t\)

where \(\alpha\) = linear expansivity of the material

\(L_0\) = Initial length of the material

\(\Delta t\) = Change in temperature

\(\therefore\) The safety gap = \(2 \times 10^{-5} \times 20 \times (75 - 25)\)

= \(2 \times 10^{-5} \times 10^3\)

= \(2 \times 10^{-2} m\)

= 0.02 m