Speed, Velocity, Acceleration.  Speed. Every motor car has a Speedometer. It generally gives the speed in Kilometers Per Hour abbreviated as KMPH. In this case the road police will definitely charge the driver. Do you know why? According to the dial the car is moving over 70 km in one hour. The road sign shows 60 km/h. The driver is violating a traffic rule. What should the driver do ? Accelerate/ Brake/ Continue. ? The driver has two options. He may release the accelerator or he can apply the brakes. After a journey or some kind of movement there are two quantities that could have been measured. One is the distance, and the other is the time taken. If a car can maintain a regular speed, the speed multiplied by the time will give give you the distance the car can travel during that time.
We usually divide the distance by the time and say we have obtained the speed. If the start was zero speed, and the speed had been varying throughout the journey. What speed do we get when we divide the distance by the time taken? You may be right. What we get is the Average Speed.
Average speed = Distance / Time. Distance and Displacement In measuring the distance the direction is not important. Displacement is a quantity that shows how much an object has got displaced in a particular direction.
 Fig. 2 The ladder is 5 m. long placed against a wall 3 m. high. Look at the Fig.2 and you will see when the man climbs the ladder he But how much can he climb? Only …3.m. That shows his vertical displacement is only 3 m. Displacement can be measured in any other direction too. For example what is man’s Horizontal displacement? Only 4 m.  Fig.3 Vertical and Horizontal Displacements. This measures the rate of change of displacement instead of a distance. In other words velocity has to be only in a particular direction whereas for speed direction may change.
As Force has a direction as well as magnitude it is also a good example of a vector Acceleration. What happens when you press the accelerator? ... Speed increases. A measurement of this change in speed is acceleration.
While velocity is the rate of change in distance, the acceleration is the rate of change in velocity. Example .1. A man runs 50 m, starting from rest toward East regularly increasing his speed taking 10 seconds. Find the following:-
Fig. 4 Uniform velocity graphs.
Fig.5 A Graph showing Acceleration.  Make your Comments on the two Graphs A and B and compare with whats given.
Formulae Symbols:- Average velocity = V. av. First velocity V 1 , Second velocity= V.2 Time = t., Displacement = d, Acceleration=a
 Q.1.0 A train 50 m. long passes a signal post in 2 seconds. Find the following: ii. What is the time it will take to pass a platform 30 m long? iiii. If the train comes to rest in 5 seconds the (negative) acceleration Q.2.0 A plane bypassing an aerodrome, cruising at 150 m.s-1 was observed for 5 s. i. What would be the displacement at cruising speed? Q.3.0  The downward velocity of a bungee jumper has been recorded and plotted as shown. i. What is the maximum velocity attained? ii. Find the positive acceleration .. iii. Find the acceleration during the reducing speed. iv. Find the height freely fallen before the chord tightens. Q. 4.0 The braking system of a car is capable of a deceleration at the rate of 6 m.s-2 Q.5.0 Examine the Velocity / Time grpha here and answer the questions below i. Find the average velocity for each second separately.
II. Find the distance traveled .
iii. Draw a displacement /Time graph.
Answer page - L to Z. Click here for answers. |
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