The calculated distance (air line) between Ostrów Mazowiecka and Mokotów is approximately 56 miles respectively 89 kilometers.
By car or train, the actual journey to Mokotów is certainly longer, as only the direct route (as the crow flies) between Ostrów Mazowiecka and Mokotów has been calculated here.
Air line (approximately)
89 kilometers
48 nautical miles