Given
The projectile is in air for a time of t=8 sec
To find
The time it takes to reach the highest point
Explanation
A projectile moves up to the highest point and then again moves down following a parabolic path.
So it will reach the highest point at a time half the time it requires to follow teh parabolic path.
The time taken to reach the highest point is 4 sec
Conclusion
The time taken is 4 sec.
Answer : The correct option is, (D) A machine does 400 joules of work in 5 seconds.
Explanation :
Power : It is defined a the rate of doing work per unit time.
Formula used :

where,
P = power
w = work done
t = time
Now we have to determine the rate of power for the following options.
(A) A machine does 200 joules of work in 10 seconds.

(B) A machine does 400 joules of work in 10 seconds.

(C) A machine does 200 joules of work in 5 seconds.

(D) A machine does 400 joules of work in 5 seconds.

From this we conclude that, a machine does 400 joules of work in 5 seconds has the highest rate of power.
Hence, the correct option is, (D)
The air resistance on the feather would be the correct answer.
Answer:
Explanation:
a=v-u/t
a=acceleration
v=final velocity
u=initial velocity
t=tme taken
we need to convert from kph to ms⁻¹
v= 150*1000/60*60= 41.67ms⁻¹
u= 120*1000/60*60= 33.33ms⁻¹
t= 2*60= 120s
a=41.67-33.33/120
a=8.34/120
a=0.0694ms⁻²