Derive the formula s = ut + 1/2 at^2, where the symbols have usual meanings. (b) A train starting from stationary position and moving with uniform acceleration attains a speed of 36 km per hour in 10 minutes.
(a) Derive the formula s = ut + 1/2 at2, where the symbols have usual meanings.
(b) A train starting from stationary position and moving with uniform acceleration attains a speed of 36 km per hour in 10 minutes. Find its acceleration.
(a) Suppose a body has an initial velocity ‘u’ and a uniform acceleration’ a’ for time ‘t’ so that its final velocity becomes ‘v’.
Let the distance travelled by the body in this time be ‘s’.
The distance travelled by a moving body in time ‘t’ can be found out by considering its average velocity. Since the initial velocity of the body is ‘u’ and its final velocity is ‘v’, the average velocity is given by:
Average velocity = \(\frac{Initial\;velocity + Final\;velocity}{2}\)
That is, Average velocity = \(\frac{u + v}{2}\)
Also, Distance travelled = Average velocity x Time
So, s = \((\frac{u + v}{2}) \times t\) ......(1)
From the first equation of motion, we have,
v = u + at
Put this value of v in equation (1), we get,
s = \((\frac{u + u + at}{2}) \times t\)
or s = \(\frac{(2u + at) \times t}{2}\)
or s = \(\frac{2ut + at^2}{2}\)
or s = ut + \(\frac{1}{2}at^2\)
where, s = distance travelled by the body in time t
u = Initial velocity of the body
and a = acceleration
Acceleration = \(\frac{Final\;velocity - Initial\;velocity}{Time\;taken}\)
So, a = \(\frac{v - u}{t}\)
= \(\frac{10 - 0}{600}\) = \(\frac{10}{600}\) m/s2
= \(\frac{1}{60}\) m/s2
= 0.016 m/s2
(b) Initial velocity, u = 0 m/s
Final velocity, v = 36km/h = 10 m/s
Time, t = 10 min = 10 x 60 = 600 sec
-
A car is travelling at 20 m/s along a road. A child runs out into the road 50 m ahead and the car driver steps on the brake pedal. What must the car’s deceleration be if the car is to stop just before it reaches the child?
3 years ago
-
A car is travelling along the road at 8 ms^-1. It accelerates at 1 ms^-2 for a distance of 18 m. How fast is it than travelling?
3 years ago
-
What type of motion is represented by each one of the following graphs?
3 years ago
-
Study the speed-time graph of a car given alongside and answer the following questions: (i) What type of motion is represented by OA? (ii) What type of motion is represented by AB?
3 years ago
-
Three speed-time graphs are given below: Which graph represents the case of: (i) a cricket ball is thrown vertically upwards and returning to the hands of the thrower?
3 years ago
- 321 Forums
- 27.3 K Topics
- 53.8 K Posts
- 0 Online
- 12.4 K Members