A body is thrown vertically upward with a velocity ‘u’. The distance travelled by it in the 7th and 8th seconds are equal. The displacement in the 8th second is equal to -(Take g = 10)

A
5m
B
2m
C
10m
D
None of these

Solution:

Concept: Formula used:

When a body is thrown vertically upwards with some velocity, the distance traveled in its 7th and 8th seconds of travel can only become equal only if it reaches its maximum height at the end of its 7th second of travel and freely falls in its 8th second.
When the body reaches its maximum height, its velocity at that point of time becomes zero. The body starts with an initial velocity equal to zero at the beginning of the 8th second and falls freely towards the ground due to the gravitational pull.
We have to compute the distance travelled by the body from the time interval 7th second till the 8th second, time duration t = 8 – 7 = 1 second.
Now we know, the displacement of a body in a time interval is given by

Here u = 0m/s, t = 1 sec and a = g = 10 m/

Hence, displacement of the body in the 8th second

=5m
Hence, option 1 is correct.