Answer 1

Slope of the x–t graph gives the velocity.
At 2.5 s, slope =\[\frac{50 - 0}{2 . 5 - 0} = 20\]

⇒ v_inst = 20 m/s
At 5 s, v_inst = 0.
At 8 s, v_inst = 20 m/s.
At 12 s, v_inst = −20 m/s.