Question

With what speed must the ball be thrown upward its returns in hand in 5 seconds

Answer 1

Free fall – velocity and distance
• If you drop a ball from
the top of a building it
gains speed as it falls.
• Every second, its
speed increases by
10 m/s.
• Also it does not fall
equal distances in
equal time intervals
0.45 4.5 1
5 50 125
4 40 80
3 30 45
2 20 20
1 10 5
0 0 0
distance
(m)
speed
(m/s)
time
(s)
Motion with constant acceleration
• A ball falling under the influence of gravity
is an example of what we call motion with
constant acceleration.
• The nice thing about this is that if we know
where the ball starts and how fast it is
moving at the beginning we can figure out
where the ball will be and how fast it is
going at any later time!
Simplest case is acceleration = 0
• If the acceleration = 0 then the velocity is
constant. [remember that acceleration is
the rate of change of velocity]
• In this case the distance an object will
travel in a certain amount of time is given
by distance = velocity x time
• For example, if you drive at 60 mph for
one hour you go 60 mph x 1 hr = 60 mi.
Example – running the 100 m dash
• Justin Gatlin won the 100 m dash in just
under 10 s. Did he run with constant
velocity, or was his motion accelerated?
• He started from rests and accelerated, so
his velocity was not constant.
• Although his average speed was about
100 m/10 s = 10 m/s, he did not maintain
this speed all through the race.
The velocity of a falling ball
• Suppose that at the moment you start
watching the ball it has an initial velocity
equal to v0
• Then its present velocity is related to the
initial velocity and acceleration by
present velocity
= initial velocity + acceleration × time
Or in symbols : v = v0 + a • t