First, let's calculate the total mechanical energy when the block is at rest and the spring is compressed 5 cm:

Now, let's use this total energy to calculate the velocity when the spring is compressed by 2.5 cm:

Therefore the speed is 1.026 m/s.
 
        
             
        
        
        
Answer: Option (b) is the correct answer.
Explanation:
It is given that a positive test charge q is released from rest at a distance r away from a charge of +Q and a distance 2r which is away from a charge of +2Q.
Then test charge to the right immediately after being released.
Therefore, the net force will be as follows.
             F = 
                = 
                = 
            F =  > 0
 > 0
Thus, we can conclude that the test charge move to the right immediately after being released.
 
        
             
        
        
        
In that case, their momentum must be equal. 
So, m1v1 = m2v2
20 * 20 = 40 * v2
v2 = 400 / 40
v2 = 10
In short, Your Answer would be: 10 m/s
Hope this helps!
        
             
        
        
        
To solve this problem we will apply the concepts related to the balance of forces. We will decompose the forces in the vertical and horizontal sense, and at the same time, we will perform summation of torques to eliminate some variables and obtain a system of equations that allow us to obtain the angle.
The forces in the vertical direction would be,



The forces in the horizontal direction would be,



The sum of Torques at equilibrium,




The maximum friction force would be equivalent to the coefficient of friction by the person, but at the same time to the expression previously found, therefore


Replacing,


Therefore the minimum angle that the person can reach is 46.9°
 
        
             
        
        
        
I) You walk barefoot on the hot street and it burns your toes. 
The road is in direct contact with your skin. Thermal energy from the road will transfer to the bottom of your feet, then to the rest of your body. This is an example of conduction.
II) When you get into a car with hot black leather in the middle of the summer and your skin starts to get burned. 
Just like in the previous example, the hot leather is in direct contact with your skin (I guess if you're going to drive naked). Thermal energy from the leather will transfe to your skin, then to the rest of your body. This is also conduction.
III) A flame heats the air inside a hot air balloon and the balloon rises. 
The flame heats air directly at the bottom of the balloon. The warm air expands and becomes less dense. This will rise and let the unheated, denser air in the balloon fall down toward the flame. This is an example of the convection cycle.
IV) A boy sits to the side of a campfire. He is 10 feet away, but still feels warm. 
The campfire heats air directly nearby. The warm air expands and moves away from the fire in all directions, leaving behind unheated, denser air to be heated up. Some of the warm air reaches the boy. This is another example of convection.
The answer is A) 1 and 2.