A spaceship drifts sideways in outer space from point $P$ to point $Q$ as shown in the figure. The spaceship is subject to no outside forces. Starting at position $Q,$ the spaceship's engine is turned on and produces a constant thrust $($force on the spaceship$)$ at right angles to the line $PQ.$ The constant thrust is maintained until the spaceship reaches another point $R$ in space. Beyond position $R,$ its speed is

continuously decreasing

constant.

increasing for a while and constant thereafter.

continuousty increasing.

constant for a while and decreasing thereafter.