A ideal pulley is connected to two blocks of masses 2kg and 4kg.The pulley is pulled up with a force of 480N.

Find the acceleration of the blocks?

without a diagram I have to guess the configuration...here is my guess

a rope pulls up on the top of the pulley with a force of 480N, the rope is attached to another rope which passes over the pulley supporting the two masses

if correct, let's go...

first, consider the sum of forces on the point of contact between the vertical rope and the rope hanging over the pulley

assuming the ropes are massless, as they almost always are in first year physics, then the sum of forces acting on that point must be zero (if the forces were non zero, the massless rope would experience an infinite acceleration)

call the tension is the same everywhere along the pulley rope and we call this tension T; this means that at the point of contact there is a force of 480N up, and a total force of 2T down

this means that the tension in the pulley rope is 240N

now, we can write newton's second law for the masses:

for each mass, there is 240N acting up, the weight acting down, and this net force = ma

for the 2 kg mass:

240N - 2.0kg*9.8m/s/s = 2a => a for the 2 kg block = 110m/s/s

for the 4 kg mass 240N - 4kg*9.8m/s/s = 4a => a=50.2m/s/s