For photoelectric emission from certain metals, the cutoff frequency is \(\nu.\) If radiation of frequency \(2\nu\)$\mathrm{}$ impinges on the metal plate, the maximum possible velocity of the emitted electron will be:
(\(m\) is the electron mass)

In Young’s double slit experiment, the slits are \(2~\text{mm}\) apart and are illuminated by photons of two wavelengths \(\lambda_1 = 12000~\mathring{A}\) and \(\lambda_2 = 10000~\mathring{A}\). At what minimum distance from the common central bright fringe on the screen, \(2~\text{m}\) from the slit, will a bright fringe from one interference pattern coincide with a bright fringe from the other?
1. \(6~\text{mm}\)
2. \(4~\text{mm}\)
3. \(3~\text{mm}\)
4. \(8~\text{mm}\)

Three blocks with masses \(m\), \(2m\), and \(3m\) are connected by strings as shown in the figure. After an upward force \(F\) is applied on block \(m\), the masses move upward at constant speed \(v\). What is the net force on the block of mass \(2m\)? (\(g\) is the acceleration due to gravity)

           
1. \(2mg\)
2. \(3mg\)
3. \(6mg\)
4. zero

A source of unknown frequency gives \(4\) beats/s when sounded with a source of known frequency of \(250~\text{Hz}.\) The second harmonic of the source of unknown frequency gives five beats per second when sounded with a source of frequency of \(513~\text{Hz}.\) The unknown frequency will be: