a ball of 100g is thrown vertically upwards with an initial speed of 150km/h, calculate the time taken to return to the thrower

pretty simple, your teacher is too easy. Mass of the ball is not material.

hf=hi+vi*t-4.9 t^2
hf=hi=0
vi given, solve for time t.

To calculate the time taken for the ball to return to the thrower, we can use the kinematic equation for vertical motion.

The equation is:

v = u + at

where:
v = final velocity (at the top, the ball's velocity will be 0)
u = initial velocity (150 km/h converts to 41.7 m/s)
a = acceleration due to gravity (-9.8 m/s^2, since the ball is moving upward against gravity)
t = time taken

In this case, we need to find the initial upward velocity. When the ball reaches its maximum height, the velocity becomes zero.

Using the equation v = u + at, we can rewrite it as:

0 = 41.7 - 9.8t

Solving for t:

9.8t = 41.7
t = 41.7 / 9.8
t ≈ 4.25 seconds

Therefore, it will take approximately 4.25 seconds for the ball to return to the thrower.