## Impulse – momentum and packing of glassware

Why are glassware packed with straw? Answer in terms of physics.

Asked Diya

**Answer:**

This is due to the impulse momentum principle

## The kinematics of a Dolphin Jump

A dolphin jumps from the surface of water and return to the surface of water after reaching the height of 1.8m.Find the initial velocity from 85km/h to 100km/h?

## Motion of a charge particle in an electric field – Numerical Problem

At t=0 a very small object with mass 0.400mg and charge +9.00μC is travelling at 125 m/s in the -x-direction. The charge is moving in a uniform electric field that is in the +y-direction and that has magnitude E= 895 N/C. The gravitational force on the particle can be neglected. How far is the particle from the origin at t= 7.99 ms.

* Hint for solving the above problem*:

displacement along X direction; x=-u_{x}t=125 x 7.99/1000

Displacement along Y direction, y=0.5 a_{y} t^{2}

a_{y}=qE/m

s=√(x^{2}+y^{2})

Just substitute the values and get the answer

## Is linear momentum conserved when a ball is thrown vertically up in the sky?

ROUNAK BHATTACHARJEE asked the above question.

The fact is that linear momentum is conserved in all interactions. If you concentrate on the motion of a single body alone, that will not account for an interaction. When thrown above, according to the principle of conservation of momentum, what we can say is that “The total momentum of the ball plus the thrower just before throwing is equal to the total momentum just after throwing”

After that what happens is controlled by the force of gravity acting on it. The force acting on it can change the momentum. Here the interaction is between the ball and the earth. On account of the huge mass of earth, the motion of earth to compensate the motion of ball and to conserve the momentum cannot be detected.

However, the linear momentum is conserved in all events and interactions so far!