Answer:
Explanation:
For sound level in decibel scale the relation is
dB = 10 log I / I₀ where I₀ = 10⁻¹² and I is intensity of sound whose decibel scale is to be calculated .
Putting the given values
61 = 10 log I / 10⁻¹²
log I / 10⁻¹² = 6.1
I = 10⁻¹² x 10⁶°¹
intensity of sound of 5 persons
= 10log 5 x 10⁶°¹
= 10( 6.1 + log 5 )
= 67.98
sound level will be 67.98 dB .
Answer:
Explanation:
Unit conversions:
1890 km/h = 1890 km/h * 1000m/km * 1/3600 h/s = 525 m/s
5.2 km = 5200 m
Assume that the jets is traveling in perfect circular motion, we can calculate the centripetal acceleration of the motion:
where v = 525m/s is the velocity of the jet and r = 5200 is the radius of the arc
a) The momentum of the coconut is 3 kg m/s
b) At first, the air resistance is negligible, so the coconut accelerates due to the force of gravity
c) The coconut reaches its terminal velocity
Explanation:
a)
The momentum of an object is given by the equation
where
m is the mass of the object
v is its velocity
For the coconut in this problem, we have:
m = 1.5 kg (mass)
v = 2 m/s (velocity)
Therefore, its momentum is
B)
There are only two forces acting on the coconut during its fall:
During the first momentums of the fall, the speed of the coconut is still low, so the air resistance is mostly negligible, and therefore only the force of gravity is acting on the coconut. Since this force is constant, it means that the acceleration of the coconut is constant: therefore, its velocity keeps increasing during the fall, and the coconut speeds up.
C)
If the tree is very tall, the fall of the coconut lasts long, and the speed of the coconut keeps increasing. Since the air resistance is proportional to the speed, this means that at some point, the air resistance is no longer negligible, and it starts to have some effect on the fall of the coconut. In particular, at a certain point, the air resistance will become equal (in magnitude) to the force of gravity (but opposite in direction): this means that from this point, the acceleration of the coconut will be zero, and therefore the coconut will continue its motion at constant velocity. This velocity is called terminal velocity, and it occurs when the force of gravity is equal to the air resistance:
where is the air resistance.
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Answer:
Speed of the ball relative to the boys: 25 km/h
Speed of the ball relative to a stationary observer: 35 km/h
Explanation:
The RV is travelling at a velocity of
Here we have taken the direction of motion of the RV as positive direction.
The boy sitting near the driver throws the ball back with speed of 25 km/h, so the velocity of the ball in the reference frame of the RV is
with negative sign since it is travelling in the opposite direction relative to the RV. Therefore, this is the velocity measured by every observer in the reference frame of the RV: so the speed measured by the boys is
v = 25 km/h
Instead, a stationary observer outside the RV measures a velocity of the ball given by the algebraic sum of the two velocities:
v = +60 km/h + (-25 km/h) = +35 km/h
So, he/she measures a speed of 35 km/h.