Jenny is traveling southward.  In order to stop, she needs a northward acceleration.
A better way to say it:
Jenny is traveling southward in her bumper car, so the direction of her velocity is south.  In order to reduce her velocity to zero, a velocity of equal magnitude but directed north must be added to it.  Then the change in velocity is positive northward, and the change in velocity per unit time is acceleration.
 
        
                    
             
        
        
        
A globe sitting on the desk can't demonstrate the speed of axial rotation 
or the speed of orbital revolution. 
        
             
        
        
        
Answer:
Option C is the correct answer.
Explanation:
Considering vertical motion of ball:-
Initial velocity, u =  2 m/s
Acceleration , a = 9.81 m/s²
Displacement, s = 40 m
We have equation of motion s= ut + 0.5 at²
Substituting
    s= ut + 0.5 at²
     40 = 2 x t + 0.5 x 9.81 x t²
    4.9t²  + 2t - 40 = 0
    t = 2.66 s   or t = -3.06 s
 So, time is 2.66 s.
Option C is the correct answer.
 
        
             
        
        
        
Answer: A thin membrane. 
Explanation:
When a sound signal is allowed to pass through the voice coil suspended between permanent magnet, magnetic field will be induced which will cause vibration in the diaphragm - a thin membrane causing disturbance of air in the surrounding of membranes which eventually produce sound waves. 
Therefore, we can conclude that a thin membrane of the loud speaker produces sound waves 
 
        
             
        
        
        
3.6 kg.
<h3>Explanation</h3>
How much heat does the hot steel tool release?
This value is the same as the amount of heat that the 15 liters of water has absorbed.
Temperature change of water:
.
Volume of water:
.
Mass of water:
.
Amount of heat that the 15 L water absorbed:
.
What's the mass of the hot steel tool?
The specific heat of carbon steel is 
.
The amount of heat that the tool has lost is the same as the amount of heat the 15 L of water absorbed. In other words,
.
.
.