Solve Free Fall Object: Find Height, Velocity & Time

In summary, the ball thrown vertically upward from the top of a building with an initial speed of 10m/s at a height of 25m from the ground reaches a maximum height of 30.1m above the ground. It strikes the ground with a velocity of 24.29m/s and takes 1.45 seconds to reach the ground. The equation V=v0+at was used to solve for the maximum height and for the velocity at impact, while the equation v=v0+(-9.8)t was used to solve for the time taken to reach the ground. The direction of the velocity and acceleration must be taken into account when plugging in values for these equations.
  • #1
bambino321
6
0
1. A ball is thrown vertically upward with an initial speed of 10m/s from thetop of a building, at a height of 25m from the ground. Assume free fall conditions.
a. To what maximum height above the ground does the ball rise?
b. With what velocity does the ball strike the ground?
c. How long does the ball take to reach the ground?


2. V=v0+at
y-y0=v0*t+1/2at^2




3. For the first part (a) i used v=v0+at and plug in my knowns
v=0, v0= 10m/s, and i solved for t which came out to be t=1.0 sec. With that i can find my maximum which I plug into the equation y-25=10(1)+(1/2)(-9.8)(1^2) and got the answer 30.1m
and for part b and c, I have no clue how to solve it if anyone can help me with a simple problem that be great
thanks for the help!
 
Physics news on Phys.org
  • #2
Part (b) is asking for a velocity. What do you know that might allow you to calculate velocity?
 
  • #3
v^2=v(int)^2+(2)(delta y)...?
 
  • #4
i found v^2=10^2+2(-9.8)(-25)
did the math and v=24.29m/s when it hits the ground
 
  • #5
OK, now part (c) asks you for a time. What do you know that could allow you to calculate time?
 
  • #6
the first equation v=v0+(-9.8)t solve for t which i have (v-v0)/(-9.8)=t
and i got -1.45s which is totally wrong since time can't be negative, I am not surewhere i have done wrong...
 
  • #7
Can I see your work? What values did you plug into the equation? (other than -9.8 m/s² of course)

By the way, time actually can be negative sometimes. Whenever you do a physics problem involving time, you have to pick some event to be t=0. If something happens before that event, it will have a negative time coordinate. It's a lot like space coordinates (x, y, z); you have to pick a point to be, say, x=0, and something that is located to the left of that point will have a negative x coordinate.

In this case I think you're right, though, that the time should be positive.
 
  • #8
i have plugged in
(24.29-10)/-9.8=-1.45
 
  • #9
Which direction is positive, up or down?

Once you figure that out, make sure the numbers you plug in have the correct signs.
 
  • #10
well it should be (24.29+10)/9.8 but I am not getting the concept, I know that 24.29 is the velocity when it hits the ground and 10 is the initial velocity so they have to be positive but I don't know about gravity since gravity is always pull downward so it has to be negative right...? if you can explain it to me that be great
 
  • #11
bambino321 said:
gravity is always pull downward so it has to be negative right...?
OK, so downward is negative, right?

Remember that velocity is a vector: it has a magnitude and a direction. What is the direction of the 10 m/s? What is the direction of the 24.29 m/s?
 

1. How do you calculate the height of a free-falling object?

To calculate the height of a free-falling object, you can use the formula h = (1/2)gt^2, where h is the height, g is the acceleration due to gravity (9.8 m/s^2), and t is the time in seconds.

2. What is the velocity of an object in free fall?

The velocity of an object in free fall can be calculated using the formula v = gt, where v is the velocity in meters per second, g is the acceleration due to gravity (9.8 m/s^2), and t is the time in seconds.

3. Can you find the time of free fall if you know the height and velocity?

Yes, the time of free fall can be calculated using the formula t = √(2h/g), where t is the time in seconds, h is the height, and g is the acceleration due to gravity (9.8 m/s^2).

4. What is the acceleration due to gravity?

The acceleration due to gravity is a constant value of 9.8 m/s^2, which represents the rate at which objects accelerate towards the Earth's surface due to the pull of gravity.

5. Is the acceleration due to gravity the same for all objects?

Yes, the acceleration due to gravity is the same for all objects, regardless of their mass or weight. This is known as the principle of equivalence and was famously demonstrated by Galileo's experiments with objects of different weights falling from the Leaning Tower of Pisa.

Similar threads

  • Introductory Physics Homework Help
Replies
3
Views
253
  • Introductory Physics Homework Help
Replies
4
Views
491
  • Introductory Physics Homework Help
2
Replies
38
Views
1K
  • Introductory Physics Homework Help
Replies
34
Views
595
  • Introductory Physics Homework Help
Replies
33
Views
837
  • Introductory Physics Homework Help
Replies
25
Views
386
  • Introductory Physics Homework Help
Replies
5
Views
204
  • Introductory Physics Homework Help
Replies
6
Views
1K
  • Introductory Physics Homework Help
Replies
15
Views
423
  • Introductory Physics Homework Help
Replies
11
Views
689
Back
Top