$A$ bird is sitting in a large closed cage which is placed on a spring balance. It records a weight of $25 \, N$. The bird (mass $m = 0.5 \, kg$) flies upward in the cage with an acceleration of $2 \, m/s^2$. The spring balance will now record a weight of ........ $N$.

$A$ plank with a box on it at one end is gradually raised about the other end. As the angle of inclination with the horizontal reaches $30^o$,the box starts to slip and slides $4.0\, m$ down the plank in $4.0\, s$. The coefficients of static and kinetic friction between the box and the plank will be,respectively:

Two cars of masses $m_1$ and $m_2$,joined back to back by a massless compressed spring,are at rest on a horizontal rough road. When the compression of the spring is suddenly removed,the cars move away from each other and come to rest due to friction. If the frictional force is the same on both cars,what is the ratio of their stopping times?

$A$ $10 \, kg$ ball attached to the end of a rigid massless rod of length $L = 1 \, m$ rotates at a constant speed in a horizontal circle of radius $r = 0.5 \, m$ and period $T = 1.57 \, s$ as shown in the figure. The force exerted by the rod on the ball is ........ $N$.

The driver of a car travelling at velocity $v$ suddenly sees a broad wall in front of him at a distance $d$. He should

In which of the following graphs,the total change in momentum is zero?