An object starting from rest travels 20 | Class 9 Science Chapter Motion, Motion NCERT Solutions

Question:

An object starting from rest travels 20 m in first 2 s and 160 m in next 4 s. What will be the velocity after 7 s from the start.

Answer:

For first 2 s motion of object,
u = 0, t = 2 s, s = 20 m.
For first 2 s motion of object,
u = 0, t = 2 s, s = 20 m 

2a = 20
a = 10 m/s^2
Next 2 s motion of object 
u = 0, s = (20 + 160) = 180 m
t = 2 + 4 = 6 sec., a = ?
Again using, s = ut + ½ at2
180 = 0 + ½ x a x (6)^2
180 = 18a 
a = 10 m/s^2
This shows that the object is moving with constant acceleration.
Total motion,
u = 0, t = 7 sec, a = 10 m/s^2, v = ?
v = u + at
v = 0 + 10 x 7
v = 70 m/s


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Welcome to the NCERT Solutions for Class 9 Science - Chapter . This page offers a step-by-step solution to the specific question from Excercise 0 , Question 20: An object starting from rest travels 20 m in first 2 s and 160 m in next 4 s. What will be the veloc....