Answer:

Explanation:
The Hi line of the Balmer series is emitted in the transition from n = 3 to n = 2 i.e.
and 
The wavelength of Hi line of the Balmer series is given by :




So, the wavelength for this line is 550 nm. Hence, this is the required solution.
Answer:
The current drawn by the motor from the line is 4.68 A.
Explanation:
Given that,
Internal resistance of the dc motor, r = 3.2 ohms
Voltage, V = 120 V
Emf in the motor, 
We need to find the current drawn by the motor from the line. A dc motor with its rotor and field coils connected in series, applying loop rule we get :

I is current drawn by the motor

So, the current drawn by the motor from the line is 4.68 A. Hence, this is the required solution.
Answer:
100Kg.m/s
Explanation:
From the question, we obtained the following information:
M= Mass = 25kg
V = Velocity = 4m/s
Momentum =?
Momentum = MV = 25x4= 100Kg.m/s
Scientists use theories to explain these things
A roller coaster is stopped on a track. When the engineer presses a launch button on the coaster, the coaster moves forward. Explain this change in terms of balanced and unbalanced forces.