A crane lifts a concrete block, whose weight is 60,000N to a height of 20m in 30s.
1 answer:
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Answer:
a) -1.25 rev/s² and 23.3 rev
b) 2.67s
Explanation:
a) ω = (500 rev/min)(1min/ 60s) => 8.333 rev/s
ω= (200 rev/min)(1min/ 60s) => 3.333rev/s
time 't'= 4 s
angular acceleration 'α'=?
constant angular acceleration equation is given by,
ω= ω
+ α
t
α= (ω
- ω
)/t => (3.333-8.333)/4
α= -1.25 rev/s²
θ-θ = ω
t + 1/2α
t²
=(8.333)(4) + 1/2 (-1.25)(4)²
=23.3 rev
b) ω=0 (comes to rest)
ω = 3.333 rev/s
α= -1.25 rev/s²
ω= ω
+ α
t
t= (ω - ω
)/α
=> (0- 3.333)/-1.25
t= 2.67s
When an electron stops, it emits a photon with energy equal to the kinetic energy lost by the electron:
The energy of the photon is
where 
is the Planck constant and f is the frequency. Therefore, the maximum frequency of the emitted photon occurs when the loss of kinetic energy is maximum.
The maximum loss of kinetic energy of the electron occurs when the electron stops completely, so it loses all its energy:
Keeping in mind that
, we have
And so, this corresponds to the energy of the emitted photon, E. Therefore, we can find the maximum frequency of the emitted photon:
The energy of the photon is
The maximum loss of kinetic energy of the electron occurs when the electron stops completely, so it loses all its energy:
Keeping in mind that
And so, this corresponds to the energy of the emitted photon, E. Therefore, we can find the maximum frequency of the emitted photon: