Answer:
a) 40 metres
b) 10 m/s (in downward direction )
c) 45 metres
d) 6 seconds
Step-by-step explanation:
Let us denote initial velocity with 'u' and acceleration due to gravity with 'g'
u=30 m/s
a) we know that s=ut+(1/2)at²
u=+30 m/s
t=4s
a=-g=-10m/s²
hence , s=30*4 +(1/2)(-10)(16) =120-80=40m
b) we know v=u+at
v=30-(10)(4) =-10m./s
Hence velocity after 4 seconds is 10 m/s in the downward direction
c) maximum height is attained when final velocity becomes 0 .
v=u+at
0=30+(-10)t
=> t=3 s
Hence at t=3 seconds, maximum height is achieved.
s=ut+(1/2)at²
s=(30)(3)+0.5*(-10)*9=45 m
Hence maximum height attained is 45 metres .
d) In the previous part we calculated that maximum height is achieved in 3 seconds. By symmetry , we can easily say that the time of flight is double the time taken to achieve the maximum height .
Hence , the time of flight is 6 seconds .