What goes up and down, but never moves?

Q. A pendulum bob of mass 50 g is suspended from the ceiling of an elevator. Find the tension in the string if the elevator (a) goes up with acceleration 1.2 m/s², (b) goes up with deceleration 1.2 m/s², (c) goes up with uniform velocity, (d) goes down with acceleration 1.2 m/s², (e) goes down with deceleration 1.2 m/s² and (f) goes down with uniform velocity.

Q. A boat goes up-stream $30$ km and down-stream $44$ km in $10$ hrs. It also goes up-stream $40$ km and down-stream $55$ km in $13$ hrs. Find the speed of the stream and the boat

Q. Doctor prescribed an old man to go regularly for a walk. He goes for some distance on first day but being on next day he goes half the distance. Similarly on each subsequent day he continues but goes only half the distances of previous day. The total distance moved by him can never exceed twice the distance moved by him on the first day.

Q. When a man stands on a moving escalator he goes up in $40s$ and when he walked up the moving escalator he goes up in $20s$. The man walk up the stationary escalator in a time of: