Step 1: Write the formula for distance in the
n-th second
The distance a freely falling object travels during the
n-th second is given by:
Sn=u+‌g(2n−1) Here,
u is the starting speed (which is 0 if just falling),
g is gravity, and
n is the second we are looking at.
Step 2: Substitute the values
We know the speed at start
u=0 and
g=10ms−2. The distance in the last but one second is 5 m , so:
5=0+‌×10(2n−1)Step 3: Solve for
nSimplify the equation:
5=5(2n−1)⇒‌=2n−1⇒1=2n−1⇒2n=2⇒n=1This means the last but one second is the 1st second of the fall.