A child stands on a weighing machine inside a lift. When the lift is going down with acceleration $\mathrm{g} / 3$, the machine shows a reading 20 N . When the lift goes upwards with acceleration $\mathrm{g} / 3$, the reading would be ( $\mathrm{g}=$ gravitational acceleration)

Which one of the following person is in an inertial frame of reference?

Force is applied to a body of mass 3 kg at rest on a frictionless horizontal surface as shown in the force against time (F-t) graph. The speed of the body after 1 s is

The pulleys and strings shown in figure are smooth and of negligible mass. For the system to remain in equilibrium, angle $\theta$ should be