Physics !!

posted by .

1) A stone is dropped from the roof of a building; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25 m/s and the two stones land at the same time.
i) How long did it take the first stone to reach the ground?
ii) How high is the building?
iii) What are the speeds of the two stones just before they hit the ground?

2)A jet fighter is traveling horizontally with a speed of 111 m/s at an altitude of 3.00×102 m, when the pilot accidentally releases an outboard fuel tank.
i) How much time elapses before the tank hits the ground
ii) What is the speed of the tank just before it hits the ground
iii) What is the horizontal distance traveled by the tank.

• Physics !! -

first stone
h=1/2 g t^2
second stone:
h=1/2 g (t-2)^2

set the equations the same, solve for time t it took the first stone
solve for height of build, h.
for speed, v^2=2gh

2. you are given h, solve for t
h=1/2 g t^2
speed is a combination of horizontal and vertical speed.
vertical=sqrt(2gh)
horizontal given

speed=sqrt(horizontal^2+vertical^2)

distance=horizontal speed*time t

• Physics !! -

can u help me solve this also ?
A car from rest and travels for 5.0 s with uniform acceleration of +1.5 m/s2. The driver then applies the brakes, causing a uniform deceleration of -2.0 m/s2. If the brakes are applied for 3.0 s.
i) How fast is the car going at the end of the braking period?
ii) How far has it gone?
iii) Sketch a graph of velocity versus time for the motion.

• Physics !! -

Hmmm.

1) If y is the stone's height at t, and h is the building height, I get

first stone: y = h - 4.9t^2
2nd stone: y = h - 25(t-2) - 4.9(t-2)^2

i: t = 5.63
the rest is easy...

• Physics !! -

For the car problem, just use your standard equations of motion.

accelerating: v = at = (1.5)(5) = 7.5
decelerating: v = 7.5 - 2(3) = 1.5

distance: 1/2 (1.5)(25) + 7.5(3) + 1/2 (-2)(9) = 32.25

• Physics !! -

1a. d1 = 0.5g*t^2 = 4.9*2^2 = 19.6 m. =
Distance fallen by the 1st stone after 2 s.

V1^2 = Vo1^2 + 2g*d
V1^2 = 0 + 19.6*19.6 = 384.16
V1 = 19.6 m/s = Velocity of 1st stone after 2 s.

d1 = d2-19.6 m.
Vo1*t + 0.5g*t^2 = Vo2*t+0.5t^2-19.6
Vo1*t-Vo2*t+4.9t^2-4.9t^2 = -19.6
19.6t-25t = -19.6
-5.4t = -19.6
Tf2 = 3.63 s. = Fall time of 2nd stone.
Tf1 = 3.63 + 2 = 5.63 s. = Fall time of
1st stone.

1b. h = Vo*t + 0.5g*t^2
h = 0 + 4.9(5.63)^2 = 155.3 m.

1c. V1^2 = Vo^2 + 2g*h
V1^2 = 0 + 19.6*155.3 = 3,043.88
V1 = 55.2 m/s.

V2^2 = 25^2 + 19.6*155.3 = 3668.88
V2 = 60.6 m/s.

Similar Questions

1. physics

A stone is dropped into a river from a bridge 41.7 m above the water. Another stone is thrown vertically down 1.87 s after the first is dropped. Both stones strike the water at the same time. What is the initial speed of the second …
2. Physics

a stone is dropped from a 75m building. when a stone has dropped 15m, a second stone was thrown downward with an initial velocity such that the two stones hit the ground at the same time. what was the initial velocity of the second …
3. physics

A stone is dropped into a river from a bridge 43.3 m above the water. Another stone is thrown vertically down 1.06 s after the first is dropped. Both stones strike the water at the same time. What is the initial speed of the second …
4. Physics

A stone is dropped from rest from the roof of a 100-m high building; 2.00 s after that, a second stone is thrown straight down with initial speed v0, and the second stone passes the first stone 21.6 m above ground. (a) When are the …
5. physics

A stone is dropped from the roof of a building; 1.60s after that, a second stone is thrown straight down with an initial speed of 26.0m/s , and the two stones land at the same time. part a. How long did it take the first stone to reach …
6. physics

A stone is dropped into a river from a bridge 45.4 m above the water. Another stone is thrown vertically down 1.14 s after the first is dropped. Both stones strike the water at the same time. What is the initial speed of the second …
7. physics

A stone is dropped into a river from a bridge 45.4 m above the water. Another stone is thrown vertically down 1.14 s after the first is dropped. Both stones strike the water at the same time. What is the initial speed of the second …
8. physics

A stone is dropped into a river from a bridge 45.4 m above the water. Another stone is thrown vertically down 1.14 s after the first is dropped. Both stones strike the water at the same time. What is the initial speed of the second …
9. physics

A stone is dropped into a river from a bridge 43.8 m above the water. Another stone is thrown vertically down 1.65 s after the first is dropped. Both stones strike the water at the same time. What is the initial speed of the second …
10. Physics

A stone is dropped from the roof of a building: 2.5s after, a second stone is thrown straight down with an initial speed of 24m/sec, and the two stones lands at the same time. (A) how long did it take the first stone to reach the ground

More Similar Questions