Question

An object starting from rest travels 20m in first 2s and 160m in next 4s. What will

be the velocity after 7s from the start? ​

Answer 1

Answer:Correct option is

D

70

From s=ut+  

2

1

​  

at  

2

 

In first 2 s,

s=20m

20=  

2

1

​  

a(2)  

2

=2a

a=10 m/s  

2

 

Velocity at the end of 2 s is  

v=u+at=0+10×2=20m/s

In next 4s, s=ut+  

2

1

​  

a  

′

t  

2

 

160=20×4+  

2

1

​  

a  

′

(4)  

2

 

80=8a  

′

 

a  

′

=10 m/s  

2

 

It shows that acceleration is uniform. From v=u+at

v=0+10×7=70 m/s  

Answer: (D) 70

Explanation:

Answer 2

After a = 10m/s square

By 2nd equation of motion,

v = u+at

v = 0 + 10 × 7

v = 70 m/s