Two blocks made of different metals identical in shape and size are acted upon by equal forces which cause them to slide on a horizontal surface. The acceleration of the second block is found to be 5 times that of the first. What is the ratio of the mass of the second to first?
Let the mass of first block = m1
acceleration of block of mass m1 = a
Let the mass of second block = m2
acceleration of block of mass m2 = 5a
Force = mass 
acceleration
Since forces are equal,
m1 a = m25a
= 
= 5
= 
20