- Chapter 1 – Measurements and Experimentation
- Chapter 2 Motion In One Dimension
- Chapter 3 Laws Of Motion
- Chapter 4 Pressure In Fluids And Atmospheric Pressure
- Chapter 5 Upthrust In Fluids Archimedes Principle And Floatation
- Chapter 6 Heat And Energy
- Chapter 7 Reflection Of Light
- Chapter 8 Propogation Of Sound Waves
- Chapter 9 Current Electricity
- Chapter 10 Magnetism
Selina Solutions Class 9 Physics Solutions for Exercise 2A in Chapter 2 - Chapter 2 Motion In One Dimension
Prev
A car is moving in a straight line with speed 18km/h. It is stopped in 5s by applying the brakes. Find: (i) the speed of the car in m/s, (ii) the retardation and (iii) the speed of the car after 2s of applying the brakes.
Given: t=5s, intial velocity=18km/hr
(i) Expressing 18km/hr to m/s
18 \mathrm{km} \mathrm{h}^{-1}=\frac{18 \times 1000 \mathrm{m}}{60 \times 60}=5 \mathrm{ms}^{-1}
(ii) As the car comes to a halt, the final velocity is 0
Retardation is negative acceleration,
\text { Retardation }=\frac{v-u}{t}=\frac{0-5}{5}=-1 \mathrm{m} / \mathrm{s}^{2}
Retardation is 1m/s^2
(iii) If ‘v’ is the speed of the car after 2s of applying brakes, then acceleration is
\begin{array}{c} \text { Acceleration }=\frac{v-\mathrm{u}}{\mathrm{t}} \\ -1=\frac{\mathrm{v}-5}{2} \\ \mathrm{v}-5=-2 \\ \mathrm{v}=3 \mathrm{m} / \mathrm{s} \end{array}
Facebook
Whatsapp
Copy Link
Lido
Courses
Quick Links
Terms & Policies
Terms & Policies
