It is easier to move anybody by pulling in than by pushing it. A body starts to move when the applied force is more than the frictional force. This frictional force is proportional to the weight of the body under which it acts. When the lawn roller is pushed by the force (F), the vertical component of the pushing force now increases the Wight (w=mg) of the roller which intern results in increase of normal reaction [R=m + F sin] and hence the friction is more.

A bus travels at a speed of 50 km/h to go from its origin of its destination at a distance of 300 km and travels at a speed of 60 km/h to return to the origin. What is the average speed of the bus?