Aptitude Test Problems in Physics Science for Everyone by S Krotov ( PDFDrive.com )

193 Aptitude Test Problems in Physics

and the sought solution is

T

1 - 1 — arccos - 13 —

T a •

Fig. 185

1.91•. Let the ball of mass m falling from a height

h elastically collide with a stationary horizontal

surface. Assuming that the time of collision of the

ball with the surface is small in comparison with

the time interval At between two consecutive colli-

sions, we obtain

As a result of each collision, the momentum of the

ball changes by Ap = 2mv = 2m)(2gh. Therefore,

the same momentum Ap = 2m 1/ 2gh. is transferred

to the horizontal surface in one collision.

In order to determine the mean farce exerted by

the ball on the horizontal surface we consider the

time interval T > At. The momentum transferred to

the horizontal surface during the time T is

2girr

AP App — 2m

1/

=mgt..

At (^) 2 V-21tIg
Consequently, the force exerted by the jumping
ball on the horizontal surface and averaged during
At=--2 "1/
2h
g