What question are you asking?
Answer:
From question (a) and (b) the pendulum motion is perpendicular to the force so the normal force will do no work and the tension in the string of the pendulum will not work

And
so

c
An example will be a where a stone is attached to the end of a string and is made to move in a circular motion while keeping the other end of the string in a fixed position
d
A dog walking along a surface which has friction, here the frictional force would acting in the direction of the motion and this would do positive work
Explanation:
Answer:
The ratio of electric field is 16:9.
Explanation:
Given that,
Radius 
Charge = Q
We know that,
The electric field is directly proportional to the charge and inversely proportional to the square of the distance.
In mathematically term,

Here, 
We need to calculate the ratio of electric field
Using formula of electric field

Put the value into the formula

Hence, The ratio of electric field is 16:9.
Answer:
5.0 m
Explanation:
The velocity of the object at time t is given by

where a=9.8 m/s^2 is the acceleration of gravity and t is the time. If we substitute v=7 m/s, we can find the time t at which the velocity became 7 m/s:

The height of the object at time t, h(t), is given by the equation

where
is the initial height. By substituting t=0.71 s inside the equation, we find the height h(t) at which the velocity is 7 m/s:
