For projectile motion on level ground assuming negligible air resistance (the initial angle being neither 0o nor 90o): can the speed ever be the same as the initial speed at a time other than at t = 0 ?

a. no

b. yes, at the end of the arch (end of trajectory)

c. yes, at its maximum height

d. yes, at half of its maximum height

B. Yes, at the end of the trajectory.

Explanation:

By the conservation of energy, in order the object to have the same speed, it must have the same potential and kinetic energy, therefore, it must be at the same height as its initial height.

b. Yes, at the end of the arch (end of trajectory)

Explanation:

according to conservation of energy and considering no air resistance:

initially the object has some kinetic energy due to speed which gets converted to gravitational potential energy till its maximum height.

since there is no energy loss, the object again gets to same amount of kinetic energy and hence the same speed.