 # Lakhmir Singh Solutions Class 9 Physics Solutions for Exercise in Chapter 1 - Motion

a) Derive the formula: \mathrm{s=ut+\frac1 2 at^2}

b) A train starting from a stationary position and moving with uniform acceleration attains a speed of 36km per hour in 10 minutes. Find its acceleration.

a) Average velocity = (initial velocity + final velocity)/2

= u + v/2

Distance travelled = (average velocity ) (time)

s = (u+v/2) (t)

s = (2u+at/2) (t)

s = (2u + at)(t)/2

\mathrm{s=2ut+\frac{at^2}{2}}

\mathrm{s=ut+\frac1 2 at^2}

Where,

s is the distance travelled by the body

t is the time taken

u is the initial velocity

v is the final velocity

b) Acceleration = final velocity – initial velocity/time taken = 0.016 \mathrm{m/s^2}

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