Answer:
The energy of the system is 15 J.
Explanation:
Given that,
Energy E = 2.5 J
Amplitude = 10 cm
We need to calculate the spring constant
Using formula of mechanical energy of the system

Put the value into the formula



If the block is replaced by a block with twice the mass of the original block
Amplitude = 6 cm
We need to calculate the energy
Using formula of mechanical energy

Put the value into the formula


Hence, The energy of the system is 15 J.
B. 1520 is the difference between their weights.
Answer:
We need 4 times more force to keep the car in circular motion if the velocity gets double.
Explanation:
Lets take the mass of the car = m
The radius of the arc = r

Given that speed of the car gets double ,v' = 2 v
Then the force on the car = F'
( radius of the arc is constant)


We know that 
Therefore F' = 4 F
So we can say that we need 4 times more force to keep the car in circular motion if the velocity gets double.
Answer:
Charge, 
Explanation:
It is given that,
Electric field strength, E = 180000 N/C
Distance from a small object, r = 2.8 cm = 0.028 m
Electric field at a point is given by :

Q is the charge on an object



So, the charge on the object is
. Hence, this is the required solution.
We know that:
F = ma,
so
F/a = constant
F₁/a₁ = F₂/a₂
F₂ = F₁ x 5.6 / 1
F₂ = 5.6F₁
If F₁ = 45 N,
F₂ = 5.6 x 45
= 252 N