Question

A stone projected from the ground level falls on the ground aftes 4 second. Then the height
of the stone 1 second after the projection (Take g = 10 m/s2) (Take g = 10 m/s2)
(1) 5 m
(2)10 m
(3) 15 m
(4)20 m​

Answer 1

Answer:

option 1 is correct.

Explanation:

As stone will take 2sec in upward motion and 2seconds in downward motion.since (h=1÷2gt^2)by using formula we get h =5.when we put t =1 sec

Answer 2

Answer:

The height of the stone one second after the projection will be equal to 15cm.  

Therefore, the option (3) is correct.

Explanation:

We have given that a stone is projected from the ground in upward direction.

The stone falls after time = 4sec

Therefore, the time of sight, T= 4s

Consider that the 'u' is the initial velocity of the stone and 'g' is the acceleration due to gravity. We know the relation:

$T=\frac{2u}{g}$

$u=\frac{T*g}{2}$

$u=\frac{(4s)(10ms^{-2})}{2}$

$u=20ms^{-1}$

Consider that 'H' is the height of stone after 1 second;

$H=ut+\frac{1}{2}(- g)t^2$                                                                     ...................(1)

Negative sign of g because stone is moving in upward direction.

Substitute the value of u, g and t in equation (1);

$H=(20)(1)+\frac{1}{2} (-10)(1)^2$

$H=20-5$

$H=15cm$

Therefore, the height of stone will be 15cm after one second from projection.