Page 82 - Physics - XI

VIVA VOCE

Q1. Which is greater—sliding friction or rolling friction?
Ans. Rolling friction is always less than sliding friction.

Q2. Why is rolling friction less than sliding friction?
Ans. Area of actual contact in case of rolling friction is less than sliding friction.

Q3. What is rolling friction?
Ans. The opposing force which comes into play when a body rolls or tries to roll over the surface of
another body is called rolling friction.

Q4. What is sliding friction?
Ans. The opposing force which comes into play when a body slides over the surface of another body is
called sliding friction.

ACTIVITY - 5

Aim
To study the variation in range of a projectile with angle of projection.

Apparatus and Materials Required

A source of water under pressure (a tap connected to a tank or water supply line), a water pipe with a metallic
nozzle (narrow opening), a large protractor, and a measuring tape

Protractor
Jet of water

60 70 80 90 100 110 120 130
50
40 140
30 150
20
10 160170 180
0
Nozzle attached with the pipe O Ground Level A
Horizontal Range, R

Fig. 5.1: Experimental setup

Principle/Theory

The horizontal distance covered by the projectile between its point of projection and the point of hitting the
ground in the same horizontal plane is called horizontal range.
Let u be the velocity of the jet of water leaving the nozzle, and it makes θ angle with the horizontal, then
the horizontal range R is given as

2
R u sin 2
g
80