$A$ body of mass $m$ dropped from a height $h$ reaches the ground with a speed of $0.8 \sqrt{gh}$. The value of work done by the air friction is $.....$

An object starts sliding on a frictionless inclined plane,and from the same height,another object starts falling freely. Which of the following statements is correct?

$A$ ball of mass $300 g$ is dropped from a height $10 m$ above a sandy ground. On reaching the ground,it penetrates through a distance $1.5 m$ in sand and finally stops. The average resistance offered by the sand to oppose the motion is (acceleration due to gravity $= 10 m s^{-2}$) (in $N$)

An object of mass $20 \,kg$ is displaced by $x = 5t^2 \,m$ (where $t$ is time) due to the application of a force. The ratio of the work done in $3 \,s$ and $5 \,s$ is:

$A$ uniform chain of mass $m$ and length $l$ is on a smooth horizontal table with $\left(\frac{1}{n}\right)^{\text{th}}$ part of its length hanging from one end of the table. The velocity of the chain,when it completely slips off the table is

Select the incorrect statement regarding the mechanical energy of a body/system.