Answer:
Work done is 0.
Explanation:
Given that,
The circumference of an orbit for a toy on a string is 18 m, r = 18 m
Centripetal force, F = 12 N
In the circular path, the centripetal force is always perpendicular to the motion of the object. Thus it makes an angle of 90 degrees with the force and displacement. Hence, we can say that the centripetal force does not do any work on the toy when it follows its orbit for one cycle.
Answer:
The ice melts mass is:

Explanation:
Kinetic Energy



Heat gained by ice= mass(g) x 80 cal
( 1 cal = 4.184 *10^7er or g cm^2/ sec^2)
Assuming no loss in heat, in the motion so both continue with temperature 0~C
To find so the mass (gm) of ice melted


As per the given Figure attached here we know that both charges q1 and q2 will apply same force on charge q3 and hence the resultant force due to both charges will be along Y axis vertically upwards
So here we know that

now from the above equation


so both of the charges will apply 0.288 N force on q3 charge along the line joining them
now the net force due to vector sum is given by

here we know that angle is

now we have


so net force on q3 is 0.46 N vertically upwards along +Y axis