First speed = 20km/h 
Time = 3 hours 
Distance = 3×20
<h3> = <u>60 km</u></h3>
Second speed = 30km/h
Time = 4 hours 
Distance = 4×30
<h3> = <u>120 km</u></h3>
Total distance = 60+120 = <u>180km</u>
Total time = 3+4 =<u> 7 hours</u> 
Average speed = 180/7
<h3> = <u>25.71</u><u> </u><u>km</u><u>/</u><u>h</u></h3>
Hope this will help... 
 
        
                    
             
        
        
        
Answer:
The answer is 1.87nm/s.
Explanation:
The  water loss must be replaced by
  water loss must be replaced by  of sap. 110g of sap corresponds to a volume of
 of sap. 110g of sap corresponds to a volume of  

thus rate of sap replacement is

The volume of sap in the vessel of length  is
 is 
 ,
,
where  is the cross sectional area of the vessel.
 is the cross sectional area of the vessel.
For 2000 such vessels, the volume is

taking the derivative of both sides we get: 

on the left-hand-side  is the velocity
 is the velocity  of the sap, and on right-hand-side
 of the sap, and on right-hand-side  ; therefore,
; therefore,

and since the cross-sectional area is
  ;
; 
therefore, 

solving for  we get:
 we get: 


which is the upward speed of the sap in each vessel.
 
        
             
        
        
        
Answer:
9.4 m/s
Explanation:
According to the work-energy theorem, the work done by external forces on a system is equal to the change in kinetic energy of the system.
Therefore we can write:

where in this case:
W = -36,733 J is the work done by the parachute (negative because it is opposite to the motion)
 is the initial kinetic energy of the car
 is the initial kinetic energy of the car
 is the final kinetic energy
 is the final kinetic energy 
Solving,

The final kinetic energy of the car can be written as

where
m = 661 kg is its mass
v is its final speed
Solving for v,

 
        
             
        
        
        
Answer:
The inner planets are smaller and rockier
Explanation:
Astronomers divide the planets into two groups in Solar system,  the  inner planets and outer planets. The inner planets are smaller and rockier and it is closer to the sun.  The outer planets are larger , further far away and made of gas
The inner planets are Mercury, Venus , Earth and Mars.  The outer planets Jupiter , Saturn , Uranus and Neptune comes after an  asteroid belt. In some other planetary systems the gas are close to the sun.
particles in a disk of gas and dust will form Planets.  If they orbit the star they are colliding and sticking.  The stars wind blows away their gases . So the nearest planets to starts are rockier.