# Physics

posted by .

Under what conditions can a quadratic function be a perfect square?

Also..
A stone is thrown vertically upward at a speed of 40m/s. How long does it take to reach a height of 90m?

I ended up with a quadratic of t^2-8t+18 which cannot be factored...So is the answer that the stone doesn't reach a height of 90m?

Another question...
A hockey player shoots a puck from his own end of the ice with an initial speed of 10 m/s. The ice surface is 60 m long and produces a deceleration of 1.0m/s^2 on the sliding puck.
a) Will the puck travel the length of the ice?
b) With what speed will it reach the far end of the ice OR how far from the end of the ice will it come to rest?

I think I used the wrong equation.
I used V2^2 = V1^2 + 2ad
And solved for distance to get 50 m which indicates that the puck didn't travel the length of the ice. But I have a feeling I did it wrong since I'm also supposed to use a kinematic equation for the second question rather than just subtraction.

Thanks!

• Physics -

I do not know what perfect square means
I guess you are using 10 instead of 9.8 for g to get round numbers. That is ok

h = 90 = 0 + 40 t -5 t^2

5 t^2 - 40 t + 90 = 0

t^2 - 8 t + 18 = 0 check

solve by completing the square or quadratic equation. I will complete the square

t^2 - 8 t = -18
t^2 - 8 t + 4^2 = -18+16
(t-4)^2 = -2
t = 4 +/- sqrt (-2)
Yes, sqrt(-2) is imaginary number. Stone does not get that high.

• Physics -

Thanks!

Can you check if I'm doing this question right and help me complete it. I'm having difficulty with the last question.

Two cars are approaching one another in the same lane of a highway. One has a speed of 30m/s, the other a speed of 20m/s when they are 96m apart. The drivers simultaneously apply brakes to avert a collision. Both cars lose speed at 6.0m/s^2. How long after the application of brakes do the cars collide? Where are the cars and at what speeds are they travelling when they collide?

dA = v1t + 1/2 at^2
= 30t - 3t^2

dB = v1t + 1/2 t^2
= 20t - 3t^2

dA+dB = 96
30t - 3t^2 + 20t - 3t^2 = 96
50t - 6t^2 = 96
- 6t^2 + 50t - 96 = 0
*dividing both sides by -2*
3t^2 - 25t + 48
Should I factor with the quadratic formula?

And then I have no idea how to answer this question -
Where are the cars and at what speeds are they travelling when they collide?

• Physics -

A hockey player shoots a puck from his own end of the ice with an initial speed of 10 m/s. The ice surface is 60 m long and produces a deceleration of 1.0m/s^2 on the sliding puck.
a) Will the puck travel the length of the ice?
b) With what speed will it reach the far end of the ice OR how far from the end of the ice will it come to rest?
++++++++++++++++++++++===
How far will it go?
v = Vo - a t = 10 - 1 t
0 = 10 - t when it stops, so it stops after 10 seconds
d = Vo t - (1/2)(1) t^2
d = 10 (10) - .5 (100)
d = 100 - 50 = 50 meters to stop.
It does not make 60 meters.
It stops after 50 meters

## Similar Questions

1. ### Physics

What do I have wrong in here? A stone is thrown vertically upward at a speed of 60.0m/s. a) How long after being thrown is it 175m above ground?
2. ### Physics

Under what conditions can a quadratic function be a perfect square?
3. ### Scientific studies

A stone is thrown vertically upward with a speed of (a) How fast is it moving when it reaches a height of 11.0 m?
4. ### physics

a girl throws a stone vertically upward with an initial speed of 8 m/s. How high will the stone rise?
5. ### PHYSICS

A stone is thrown in a vertically upward direction with a velocity of 5 m s -1 . If the acceleration of the stone during its motion is 10 m s-2 in the downward direction, what will be the height attained by the stone and how much time …
6. ### Physics

A stone is thrown vertically upward with a speed of 18.0 m/s. (a)How fast is it moving when it reaches a height of 11.0 m?
7. ### Physics

A stone is thrown vertically upward with a speed of 12.0 m/s. (a) How fast is it moving when it reaches a height of 5.0 m?
8. ### physics

a stone is thrown vertically upward at a speed of 10 m/s from a cliff that is 95m high. How long will it take the stone to reach the bottom?
9. ### Physics

A stone is thrown vertically upward with a speed of 21.0 m/s a)How fast is it moving when it reaches a height of 15.8 m b)How much time is required to reach this height?
10. ### physics

a stone is thrown vertically upward an initial velocity of 12m/s from the top of a building . it takes 3.4s for the stone to hit the ground a. find the height of the building b. find the maximum height that the stone will reach c. …

More Similar Questions