The mass of a body measured by a physical balance in a lift at rest is found to be $m$. If the lift is going up with an acceleration $a$,its mass will be measured as

Select the correct statement regarding pseudo force.

$A$ ball is suspended on a thread from the ceiling of a car. The brakes are applied and the speed of the car changes from $5\, m/s$ to $\frac{5}{3}\, m/s$ during the time interval of $3\, s$. The angle that the thread will deviate from the vertical in the new equilibrium position is:

Two wooden blocks of masses $M$ and $m$ are placed on a smooth horizontal surface as shown in the figure. If a force $P$ is applied to the system as shown in the figure such that the mass $m$ remains stationary with respect to the block of mass $M$,then the magnitude of the force $P$ is

$A$ car is moving with a uniform speed on a level road. Inside the car,there is a balloon filled with helium and attached to a piece of string tied to the floor. The string is observed to be vertical. The car now takes a left turn while maintaining the same speed on the level road. The balloon in the car will:

$A$ block of mass $m$ moving with a velocity $v_0$ on a smooth horizontal surface strikes and compresses a spring of stiffness $k$ until the mass comes to rest,as shown in the figure. This phenomenon is observed by two observers:
$A$: standing on the horizontal surface
$B$: standing on the block
To an observer $B$,when the block is compressing the spring: