Question

Antonina throws a coin straight up from a height of

1

.

2

m

1.2m1, point, 2, space, m above the water surface in a fountain. The coin strikes the water

1

.

3

s

1.3s1, point, 3, space, s later. We want to know the vertical velocity of the coin at the moment it strikes the water. We can ignore air resistance.

Which kinematic formula would be most useful to solve for the target unknown?

Answer 1

`s=vt-(1)/(2)gt^2`

Step-by-step explanation:

We could use the following suvat equation:

`s=vt-(1)/(2)gt^2`

where

s is the vertical displacement of the coin

v is its final velocity, when it hits the water

t is the time

g is the acceleration of gravity

Taking upward as positive direction, in this problem we have:

s = -1.2 m

`g=-9.8 m/s^2`

And the coin reaches the water when

t = 1.3 s

Substituting these data, we can find v:

`v=(s)/(t)+(1)/(2)gt=-(1.2)/(1.3)+(1)/(2)(-9.8)(1.3)=-7.3 m/s`

where the negative sign means the direction is downward.