**In text Questions of page no 103**

**Q. No 1: When will you say a body is in (i) uniform acceleration? (ii) non-uniform acceleration?**

Ans:

(i) A body is said to have uniform acceleration if it travels in a straight path and the velocity of a body increases or decreases by equal amounts in an equal interval of time.

(ii) A body is said to have non-uniform acceleration if it travels in a straight and the velocity of a body increases or decreases in unequal amounts in an equal interval of time.

**Q. No 2: A bus decreases its speed from 80 km h**^{-1} to 60 km h^{-1} in 5 s. Find the acceleration of the bus.

Ans:

Initial velocity of the bus, u = 80 km/h

$ = 80 \times {5 \over {18}} = 22.22m/s$

Final velocity of the bus, v = 60 km/h

$ = 60 \times {5 \over {18}} = 16.67m/s$

Time take (t) = 5 s

Now acceleration(a)

$\eqalign{ & = {{v - u} \over t} \cr & = {{16.67 - 22.22} \over 5} \cr & = {{ - 5.55} \over 5} \cr & = - 1.11m{s^{ - 2}} \cr} $

when acceleration is negative then it is called retardation.

**Q. No 3: A train starting from a railway station and moving with uniform acceleration attains a speed 40 km h**^{-1} in 10 minutes. Find its acceleration.

**Ans:**

Initial velocity of the train (u) = 0 m/s

Final velocity of the train, v = 40 km/h

= 40×5/18=100/9 m/s

Time taken, t = 10 min = 10 × 60 = 600 s

Now, acceleration

$\eqalign{ & a = {{v - u} \over t} \cr & = {{{{100} \over 9} - 0} \over {600}} \cr & = {{100} \over {9 \times 600}} \cr & = {1 \over {54}}m/{s^2} \cr} $