Seven
The magnitude is pointing towards the origin and is at - 20 degrees. The combination makes 160 with the x axis: C answer
Eight
They keep doing this. They use distance where they should use displacement but they use distance to try and fool you. It's a mighty poor practice.
The distance between the start and end points is the displacement. That "distance" is 180*sqrt(25) = 900 . The actual distance should be 180*4 + 180*3 = 720 + 540 = 1260. That's what a car's odometer or a bicycle odometer would read.  the difference is 360. 
I really do object to the wording, but what can I do?
Nine
Nine is the same thing as 8. 
Displacement = sqrt(400^2 + 80^2)= sqrt(166400) = 408
The actual distance is 400 + 80 = 480
The difference is the answer = 480 - 408 = 72 <<<< Answer 
Ten
This is just the displacement magnitude.
dis = sqrt(30^2 + 80^2)
dis = sqrt(900 + 6400)
dis = sqrt(7300)
dis = 85.44 <<<< Answer D
Twelve
Vi =  2.15*Sin(30) = 1.075 m/s
vf = 0
a = - 9.81
t = ?
<u>Formula</u>
a = (vf - vi)/t
<u>Solve</u>
-9.81 =  (0 - 1.075)/t
- 9.81 * t = -1.075
t = 0.11 seconds
Thirteen
I'm leaving this last one to you. You need the initial height xo to answer it properly. Judging by the other questions, this one is right.
Edit
That is a surprise! Really quickly
d = 3.2 m
a = - 9.82
vf = 0
vi = ?
vf^2 = vi^2 - 2*a*d
0 = vi^2 - 2*9.81*3.2
vi = sqrt(19.62*3.2)
vi = 8.0  m/s   But that is the vertical component of the speed
v = vi/sin(25)
v = 8.0/sin(25) = 11
 
        
             
        
        
        
Answer:
The average acceleration is 16.6 m/s² ⇒ 1st answer
Explanation:
A rocket achieves a lift-off velocity of 500.0 m/s from rest in 
30.0 seconds
The given is:
→ The initial velocity = 0
→ The final velocity = 500 meters per seconds
→ The time is 30 seconds
Acceleration is the rate of change of velocity of the rocket
→ 
where a is the acceleration, v is the final velocity, u is the initial velocity
and t is the time
→ u = 0 , v = 500 m/s , t = 30 s
Substitute these values in the rule
→  m/s²
 m/s²
<em>The average acceleration is 16.6 m/s²</em>
 
        
             
        
        
        
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<h2>The pressure will become double </h2>
Explanation:
The gas pressure is directly proportional to the mean root square velocity of the constituent molecules of gas .
P ∝  I
      I
Here C₁ , C₂ ------------ Cₙ is the velocities of molecules .
By making these velocities double 
The pressure P₀ ∝ 2 II
          II
By dividing II by I 
P₀ = 2 P
Thus pressure will become double than its previous value 
 
        
             
        
        
        
Answer:
 and
 and 
Explanation:
According to Coulomb's law, the magnitude of  force between two point object having change  and
 and  and by a dicstanced is
 and by a dicstanced is

Where,  is the permitivity of free space and
 is the permitivity of free space and 
 in SI unit.
 in SI unit.
Before  dcollision:
Charges on both the sphere are  and
 and  , d=20cm=0.2m, and
, d=20cm=0.2m, and  N
 N
So, from equation (i)


After dcollision: Each ephere have same charge, as at the time of collision there was contach and due to this charge get redistributed which made the charge density equal for both the sphere t. So, both have equal amount of charhe as both are identical.
Charges on both the sphere are mean of total charge, i.e 

 d=20cm=0.2m, and  N
 N
So, from equation (i)



As given that the force is repulsive, so both the sphere have the same nature of charge, either positive or negative, so, here take the magnitude of the charge.


The equation (ii) become:



From equation (iii)

So, the magnitude of initial charges on both the sphere are  Coulombs
 Coulombs and
 and  Colombs or
 Colombs or  .
.
Considerion the nature of charges too, 
 and
 and 