- 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 2C in Chapter 2 - Chapter 2 Motion In One Dimension
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A body moving with a constant acceleration travels the distances 3m and 8m respectively in 1s and 2s. Calculate: (i) the initial velocity, and (ii) the acceleration of the body.
Let distance travelled in time t1=1s be s1=3m
Let distance travelled in time t2=2s be s2=8m
We know that s = ut+\frac{1}{2}at^2
, substituting for s1 and s2 is:
S1= ut_1+\frac{1}{2}at_1^2
and S2= ut_1+\frac{1}{2}at_2^2
Subtracting s1 from s2, we get;
S2-S1 = u(t2-t1) + 1/2a (t2 x t2 – t1 x t1)
8-3 = u(2-1) + 1/2 a(4-1)
5 = u + 3/2a
a = (10-2u)/3 - equation 1
use this value of ‘a’ obtained in the equation for S1, we get;
S1= ut_1+\frac{1}{2}at_1^2
3=u(1 x 1) + ½ [(10-2u)/3](1 x 1)
3 = u + 10−2𝑢 / 6
18= 6u + 10 – 2u
u =2m/s
using the value of u obtained in equation 1, we get;
a= (10-2u)/3
a=6/3
a=2 m/s^2
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