The Student Room Group

Understanding A SUVAT Question

Question:
A stone is thrown vertically upwards with the speed 15m/s from a point h above the ground

The stone hits the ground 4 seconds later

(a) Find the value of h

This is a typical question and I went about it by doing
s = -h
u = 15
a = -g
t = 4

Subbed the values into s = ut + 1/2at^2 to get the answer.

My question:

Why do you sub in t = 4 if s = -h shouldn't it be some value less than 4? It shouldn't take 4 seconds to travel h to the ground.

Thank You
(edited 5 years ago)
Original post by Grant Thompson
Question:
A stone is thrown vertically upwards with the speed 15m/s from a point h above the ground

The stone hits the ground 4 seconds later

(a) Find the value of h

This is a typical question and I went about it by doing
s = -h
u = 15
a = -g
t = 4

Subbed the values into s = ut + 1/2at^2 to get the answer.

My question:

Why is S equal to -h?
Why is t = 4 if s = -h shouldn't be some value less than 4?

Thank You


Well the place is h metres above the ground. You're looking at the time the stone hits the ground. At this time, the displacement of the ball is h metres under from where it was projected. So s = -h since it's at a lower position.

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