A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from?How can it be corrected?

A trolley of mass 200 kg moves with a uniform speed of 36 km/ h on a frictionless track. A child of mass 20 kg runs on the trolley from one end to the other (10 m away) with a speed of 4 m s^-1 relative to the trolley in a direction opposite to the its motion, and jumps out of the trolley. What is the final speed of the trolley? How much has the trolley moved from the time the child begins to run?

A person cannot see objects nearer than 1.5 m from his eyes while a person with normal vision can see objects upto 25 cm from his eyes. What is the nature and power of the, lens required to correct this defect?

With what velocity a body has to be thrown up so that it can rise up to a height of 10 metres from the ground? How much time will fake to reach the highest point?