Answer:
A jet plane flying straight and at level at constant speed
Explanation:
      The<em> inertial frame </em>of reference is a frame of reference in which all <em>Newton law  is valid</em> ie Newton second law of motion and therefore newton first law of motion holds good. <em>The frame of reference does not accelerate.</em>
All the object that is in the frame of reference are at rest or moving with constant rectilinear motion with constant velocity unless acted upon by any force.
 
        
             
        
        
        
<h2>
The answer got is reasonable.</h2>
Explanation:
We have equation of motion v² = u² + 2as
Initial velocity, u = 300 m/s  
Acceleration, a = ?
Final velocity, v = 400 m/s  
Displacement,s = 4 km = 4000 m
Substituting  
v² = u² + 2as
400² = 300² + 2 x a x 4000
a = 8.75 m/s² = 8.8 m/s²
The acceleration is 8.8 m/s²
The answer got is reasonable.
 
        
        
        
We assume that horn releases sound of constant frequency. In order for observer to observe different frequency either horn or observer or both must move.
This happens due to Doppler effect. It states that when position of source of sound and observer relative to each other changes, the observed frequency also changes. If the source emits sound of constant frequency than observed frequency will be either higher or lower than original.
When distance between source and observer increases the observed frequency will be lower. This is because same number of sound waves must cover greater distance so they have greater wavelength.
When distance between source and observer decreases the observed frequency will be higher. This is because same number of sound waves must cover smaller distance so they have smaller wavelength. 
Wavelength and frequency are inversely proportional meaning when one increases the other drecreases.
From this explanation we can find answer for our question. <span>If we wanted the pitch of a horn to drop relative to an observer we need to move horn away from an observer.</span>
        
             
        
        
        
Answer:
v(t)= (d/dt)x(t)
Explanation:
The instantaneous velocity of an object is the limit of the average velocity as the elapsed time approaches zero, or the derivative of x with respect to t. Like average velocity, instantaneous velocity is a vector with dimension of length per time. The instantaneous velocity at a specific time point  t
0  is the rate of change of the position function, which is the slope of the position function  
x
(
t
)
at  t
0
.
 
        
             
        
        
        
Answer: Option (A) is the correct answer.
Explanation:
Laser helps in zooming an image on which it is directed or falls so that it becomes easier for a large population to understand what the teacher or guide is talking about.
For example, when Greg is giving slide show presentation to a large audience then in order to make his slides visualized by everyone in the room he uses laser.
Therefore, we can conclude that a laser best help him with the presentation as he can use the laser to enlarge images on the slides.