Experimental investigations on ablatively accelerated thin plastic foil targets irradiated by a 6J, 5 nsec Nd: glass laser pulse, were conducted using shadowgraphy technique. A 2 nsec, 0.53 µm probe pulse, derived from the main laser was used for recording the foil motion. It was observed that 6 µm plastic foils could be accelerated to a velocity of about 3 × 10⁶ cm/sec for an incident laser intensity of 5 × 10¹³ W/cm² and the corresponding ablation pressure was 0.4 Mbar. Ablation pressure (P) scaling against absorbed laser intensity (I_a) was slower (P ∝I_a^0.4) for a smaller laser focal spot (30 µm) as compared to the scaling (P ∝I_a^0.7) for a larger focal spot (500 µm). This result has been explained considering the loss due to lateral energy transport from the laser plasma interaction region.