# physics

posted by .

A ball is thrown vertically upwards with an initial velocity of 20.96 m/s. Neglecting air resistance, how long is the ball in the air? What is the greatest height reached by the ball?

this problem seems easy enough but I can't seem to get the answer. How can I get time using only velocity?

• physics -

Two equations for constant acceleration:
v = Vo + a t
x = Xo + Vo t +(1/2) a t^2
here
a = -9.8 m/s^2
Vo = 20.96
Xo = 0
when v = 0, we are at the top
solve for t at the top (t at the ground again will be twice that by the way)
Then use that t at the top in the second equation
x = 0 + 20.96 t -4.9 t^2
to get the height at the top

if you did not belive me about doubling that t at the top to get t when it hits the ground again, there are two ways to proceed.
Way 1
let the ball drop with zero initial velocity from the top (you will see why the time falling is the same as the time rising)
Way 2
solve the second equation for t when x= 0,
of course t = 0 and t = something which I hope is t = twice t at the top should be solutions to the quadratic.

## Similar Questions

1. ### physics

A ball is thrown vertically upwards, from ground level, with an initial speed vo. Assume that air resistance is negligible so that the acceleration of the ball is due solely to gravity. a) Derive an algebraic formula for the time t …
2. ### physics

A soccer ball is kicked into the air at an angle of 38 degrees above the horizontal. The initial velocity of the ball is +30.0m/s. How long is the ball in the air?
3. ### physics

a soccer ball is kicked into the air at an angle of 38 degrees above the horizontal. The initial velocity of the ball is 30.0m/s. How long was the ball in the air?
4. ### physics

a soccer ball is kicked into the air at an angle of 38 degrees above the horizontal. The initial velocity of the ball is 30.0m/s. How long was the ball in the air?
5. ### physics

a soccer ball is kicked into the air at an angle of 38 degrees above the horizontal. The initial velocity of the ball is 30.0m/s. How long was the ball in the air?
6. ### Physics

A ball is thrown vertically upwards with an initial velocity of 27.0 m/s. Neglecting air resistance, how long is the ball in the air?
7. ### Physics

A ball is thrown vertically upwards with an initial velocity of 27.0 m/s. Neglecting air resistance, how long is the ball in the air?
8. ### kinetics

a ball of mass 200 g is thrown vertically upwards with a velocity of 20ms-1 ignoring air resistance. a) calculate the kinetic energy of the ball as it is released b)calculate the maximum height reached by the ball c) state the velocity …
9. ### kinetics

a ball of mass 200 g is thrown vertically upwards with a velocity of 20ms-1 ignoring air resistance. a) calculate the kinetic energy of the ball as it is released b)calculate the maximum height reached by the ball c) state the velocity …
10. ### Physics

A ball thrown vertically upwards is caught by the thrower 8 seconds afterwards . (take g =10) When the ball is caught by the thrower: what is its displacement from the initial position?

More Similar Questions