$A$ person walks up a stalled escalator in $90 \ s$. When standing on the same moving escalator,he reaches the top in $60 \ s$. The time it would take him to walk up the moving escalator will be: (in $s$)

When is the relative velocity of two cars moving with unequal velocities less than the individual velocity of either car?

$A$ boy throws a ball in the air at $60^{\circ}$ to the horizontal,along a road with a speed of $10 \, m/s$. Another boy sitting in a passing car observes the ball. Sketch the motion of the ball as observed by the boy in the car,if the car has a speed of $18 \, km/h$. Give an explanation to support your diagram.

$A$ jet airplane travelling at the speed of $500 \; km \; h^{-1}$ ejects its products of combustion at the speed of $1500 \; km \; h^{-1}$ relative to the jet plane. What is the speed of the latter with respect to an observer on the ground?

$A$ boat is moving with a velocity of $3\hat i + 4\hat j$ in a river,and the water is moving with a velocity of $-3\hat i - 4\hat j$ with respect to the ground. The relative velocity of the boat with respect to the water is:

Particle $A$ moves along the $X$-axis with a uniform velocity of magnitude $10 \ m/s$. Particle $B$ moves with a uniform velocity of $20 \ m/s$ along a direction making an angle of $60^{\circ}$ with the positive direction of the $X$-axis as shown in the figure. The relative velocity of $B$ with respect to $A$ is