Question

v>u (ii) v<u (iii) v = u (iv) none of these
18. Read the following and answer the questions from 19 (a) to 19 (e)
The rate of change of velocity is known as its acceleration. The SI unit to measure acceleration
(a) The acceleration of a body is said to be positive if
(i) v>u (ii) v<u (ii) v = u (iv) none of these
(b) The acceleration of a body is said to be negative if
is m/s^2. Formula for acceleration is, a =
: (v - u)/t
(i)
(c) The acceleration of a body is said to be zero if
(i) v>u (ii) v<u (iii) v = u (iv) none of these
(d) Out of the following, which is an example of uniform acceleration
(i) the motion of a football player on the field
(ii) a body falling freely from a height towards the surface of the earth.
(ii) a car running on the road (iv) a boy moving along a circular track
(e) A jeep starts from rest and attains a speed of 36 m/s in 10 seconds. Calculate the
acceleration.
(i) 3.6 m/s^2 (ii) 3600 m/s^2 (iii) -3.6 m/s^2 (iv) -3600 m/s^2​

Answer 1

Firstly let us know something about acceleration, then further solve!

$\begin{gathered}\boxed{\begin{array}{c}\\ \bf What \: is \: acceleration? \\ \\ \sf The \: rate \: of \: change \: of \: velocity \: of \: an \\ \sf object \: with \: respect \: to \: time \\ \sf is \: known \: as \: acceleration. \\ \\ \sf \star \: Negative \: acceleration \: is \: known \: as \: deceleration. \\ \sf \star \: Deceleration \: is \: known \: as \: retardation. \\ \sf \star \: It's \: SI \: unit \: is \: ms^{-2} \: or \: m/s^2 \\ \sf \star \: It \: may \: be \: \pm ve \: or \: 0 \: too \\ \sf \star \: It \: is \: a \: vector \: quantity \\ \\ \bf Conditions \: of \pm ve \: or \: 0 \: acceleration \\ \\ \sf \odot \: Positive \: acceleration: \: \sf When \: \bf{u} \: \sf is \: lower \: than \: \bf{v} \\ \sf \odot \: Negative \: acceleration: \: \sf When \: \bf{v} \: \sf is \: lower \: than \: \bf{u} \\ \sf \odot \: Zero \: acceleration: \: \sf When \: \bf{v} \: \sf and \: \bf{u} \: \sf are \: equal \end{array}}\end{gathered}$

Required solution:

a) The rate of change of velocity is known as its acceleration.

• The above statement is true.

The SI unit to measure acceleration is metre per second sq. that is ${\sf{m/s^2 \: or \: ms^{-2}}}$

b) The acceleration of a body is said to be positive if v > u Therefore, option (i) is right option.

c) The acceleration of a body is said to be negative if v < u

d) Formula for acceleration is = a = (v-u)/t that is ${\sf{a \: = \dfrac{v-u}{t}}}$

e) The acceleration of a body is said to be zero if v = u Therefore, option (iii) is correct option.

f) Out of the following, which is an example of uniform acceleration

• The motion of a football player on the field.

• A body falling freely from a height towards the surface of the earth.

• A car running on the road

• A boy moving along a circular track

Solution: A body falling freely from a height towards the surface of the earth is an example of uniform acceleration.

And the all other are examples of non uniform acceleration.

g) A jeep starts from rest and attains a speed of 36 m/s in 10 seconds. Calculate the acceleration.

Provided that:

• Initial velocity = 0 m/s
• Final velocity = 36 m/s
• Time taken = 10 seconds

To calculate:

• The acceleration

Solution:

• The acceleration = 3.6 m/s²

Using concept:

• Acceleration formula

Using formula:

• ${\sf{a \: = \dfrac{v-u}{t}}}$

Where, a denotes acceleration, v denotes final velocity, u denotes initial velocity and t denotes time taken

Required solution:

$:\implies \sf a \: = \dfrac{v-u}{t} \\ \\ :\implies \sf a \: = \dfrac{36-0}{10} \\ \\ :\implies \sf a \: = \dfrac{36}{10} \\ \\ :\implies \sf a \: = 3.6 \: ms^{-2} \\ \\ :\implies \sf Acceleration \: = 3.6 \: ms^{-2}$

Therefore, acceleration is 3.6 metre per second sq. Henceforth, option (i) is correct