Question

1. A particle projected vertically upward returns to point of projection in 4 seconds. The initial speed of projection will be

a) 10 m s–1
b) 20 m s–1
c)40 m s–1
d)80 m s–1
2. If a particle starts from rest and moves with constant acceleration 2 m/s2, then displacement during first 10 s of its motion is
a)100 m
b)10 m
c)20 m
d)50 m

Answer 1

(b) is the correct answer

If the acceleration is 10 m/s^2 then in two seconds the particle will go from 20 m/s to zero speed.

In the next two seconds the particle will go from zero speed to 20 m/s.

The speeds must be equal to satisfy conservation of energy.