Distance unknown, have acceleration time and another distance

In summary: When you substituted the value of vi back into the same equation, you did a sign mistake again. :redface:Moreover, you aren't asked the initial velocity in the question. :smile:You are asked how high it would go above the window.For that you need to find the maximum height the stone can achieve.(Hint: Velocity at maximum height is 0m/s).
  • #1
vicsic
13
0

Homework Statement



A rock is thrown up past a window. The rock requires 0.20 s to completely pass by the 1.4 m window calculate the height above the window the rock would travel.

Homework Equations



D=vf(t) -1/2at^2

The Attempt at a Solution



I have tried using the acceleration as 9.81 m/s and 7 m/s and the vf as i got that from 1.4/0.20. It does not give me the right answer though. any help would be great!
 
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  • #2
What you are given is time for completing 1.4m is 0.2s, can you find the initial velocity of stone using this data? :smile:
 
  • #3
So i found that the initial velocity is 6.019 m/s now how does that lead me to how far above the window the rock will travel?
 
  • #4
I don't get my answer to be 6.019m/s. :redface:

Show me the steps you followed. :smile:
 
  • #5
Pranav-Arora said:
I don't get my answer to be 6.019m/s. :redface:

Show me the steps you followed. :smile:

1.4m=vi(.20)+1/2(9.81)(0.20)^2
1.4=vi(0.20)+.1962
1.2038=vi(0.20)
vi=6.019m/s
 
  • #6
vicsic said:
1.4m=vi(.20)+1/2(9.81)(0.20)^2
1.4=vi(0.20)+.1962
1.2038=vi(0.20)
vi=6.019m/s

Ah...there you go wrong.
The direction of acceleration which is g in our case is opposite to the initial velocity.
Initial velocity is in upward direction and acceleration is in downward direction. So one has to be negative. That means you didn't take care of signs. If you choose upward as positive then downward direction has to be negative.

Try again & post the steps here. :smile:
 
  • #7
Pranav-Arora said:
Ah...there you go wrong.
The direction of acceleration which is g in our case is opposite to the initial velocity.
Initial velocity is in upward direction and acceleration is in downward direction. So one has to be negative. That means you didn't take care of signs. If you choose upward as positive then downward direction has to be negative.

Try again & post the steps here. :smile:

Got the answer!

1.4m=vi(0.20)+1/2(-9.81)(0.20)^2
1.4m=vi(0.20)-0.1962
1.5962=vi0.20
vi=7.981 m/s

then plugging it back in

d=vi(t)+1/2at^2
d=7.981(0.20)+1/2(9.81)(0.20)^2
d=1.7924
d=1.8m

thanks for the help :)
 
  • #8
vicsic said:
Got the answer!

1.4m=vi(0.20)+1/2(-9.81)(0.20)^2
1.4m=vi(0.20)-0.1962
1.5962=vi0.20
vi=7.981 m/s

then plugging it back in

d=vi(t)+1/2at^2
d=7.981(0.20)+1/2(9.81)(0.20)^2
d=1.7924
d=1.8m

thanks for the help :)

You're still incorrect. :)

When you substituted the value of vi back into the same equation, you did a sign mistake again. :redface:

Moreover, you aren't asked the initial velocity in the question. :smile:
You are asked how high it would go above the window.
For that you need to find the maximum height the stone can achieve.
(Hint: Velocity at maximum height is 0m/s).

Try again and post the steps here. :)
 

1. What is the formula for calculating distance when acceleration and time are known?

The formula for calculating distance when acceleration and time are known is d = 1/2 * a * t^2, where d is the distance, a is the acceleration, and t is the time.

2. How does acceleration affect the distance traveled?

Acceleration directly affects the distance traveled by an object. The greater the acceleration, the greater the change in velocity and therefore the greater the distance traveled in a given amount of time.

3. Can you calculate the distance without knowing the acceleration and time?

No, the distance cannot be calculated without knowing the acceleration and time. These two variables are necessary in the formula for calculating distance.

4. What units should be used when calculating distance with acceleration and time?

The units for distance will depend on the units used for acceleration and time. If acceleration is given in meters per second squared (m/s^2) and time is given in seconds (s), then the distance will be in meters (m).

5. How does changing the acceleration or time affect the distance traveled?

Changing the acceleration or time will directly affect the distance traveled. Increasing the acceleration or time will result in a greater distance traveled, while decreasing the acceleration or time will result in a shorter distance traveled.

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