Calculating Average Speed of Ball in First 5 Seconds

  • Thread starter schyuler2
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In summary, the average speed of a ball thrown straight upward with a speed of 30 m/s in the first 5 seconds is 13.9 m/s. The total distance traveled by the ball during this time is 63.9 m. It travels 45.9 meters up and then 23.4 meters down.
  • #1
schyuler2
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Homework Statement


A ball is thrown straight upward from the ground with a speed of 30 m/s. What is the average speed of the ball in the first 5 seconds?


Homework Equations


VBy2 = VAy2 + 2(ay) * dABy

VBy = VAy + ay * change in time

Average velocity = dABy / change in time

The Attempt at a Solution


VBy2 = VAy2 + 2(ay) * dABy
(0)2 = (30)2 + 2(9.8) * dABy
0 = 900 + 19.6 * daby
-900 = 19.6 *dABy
-45.9 = dABy
^but dABy can't be negative. what am i doing wrong?

also-- do i use "5 sec" for my time interval on the other equations? i cannot figure out what it means by "first 5 seconds." HELP
 
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  • #2
schyuler2 said:

Homework Statement


A ball is thrown straight upward from the ground with a speed of 30 m/s. What is the average speed of the ball in the first 5 seconds?


Homework Equations


VBy2 = VAy2 + (that should be a minus sign, not a plus sign)2(ay) * dABy

VBy = VAy + ay * change in timewatch your minus signs

Average velocity = dABy / change in time
the problem asks for average speed, which is not the same as average velocity

The Attempt at a Solution


VBy2 = VAy2 + 2(ay) * dABy
(0)2 = (30)2 + 2(9.8) * dABy
0 = 900 + 19.6 * daby
-900 = 19.6 *dABy
-45.9 = dABy
^but dABy can't be negative. what am i doing wrong?
once you make your minus sign correction, 45.9 m is the distance traveled up. How long did it take to reach that distance? Where will the ball be after 5 seconds? What total distance will the ball have traveled in that 5 seconds (45.9 meters up and an additional distance down)? Then average speed is ?
 
  • #3
well if it travels a total of 2*45.9m ... then the dABy = 91.8

so:
average velocity = dABy / t
= 91.8/5
=18.36 m/sec
?
 
  • #4
schyuler2 said:
well if it travels a total of 2*45.9m ... then the dABy = 91.8

so:
average velocity = dABy / t
= 91.8/5
=18.36 m/sec
?
No, first off, you are looking for average speed, after 5 seconds. You can use y = V_yo(t) - 1/2gt^2 (where t=5) to find out the position of the ball after 5 seconds ( it'll be on its descent at that point). Then calculate the average speed by first calculating the total distance it has traveled during that time.
 
  • #5
Thanks! so,
y =V_yo(t) - 0.5gt^2
y = 30(5) - 0.5 (9.8) (5)^2
y = 150 - 4.9 * 25
y = 150 - 122.5
y = 27.5 m

then...
Vavg = dABy / t
Vavg = 27.5 m /5 sec
Vavg = 5.5 m/sec
 
  • #6
schyuler2 said:
Thanks! so,
y =V_yo(t) - 0.5gt^2
y = 30(5) - 0.5 (9.8) (5)^2
y = 150 - 4.9 * 25
y = 150 - 122.5
y = 27.5 m

then...
Vavg = dABy / t
Vavg = 27.5 m /5 sec
Vavg = 5.5 m/sec
You are getting close, but again, the problem is asking for average speed, not average velocity. What you have calculated is the average velocity, which is displacement divided by time, a vector quantity. Average speed is distance traveled divided by time, a scalar quantity. It travels 45.9 m up and then (45.9 - 27.5) m down, for a total distance of ____? and an average speed of _______?
 
  • #7
Total distance: 45.9 + 23.4 = 63.9 m

avg speed = dist/time
avg speed = 63.9 m / 5 sec
avg speed = 13.9 m/sec^2
 
  • #8
45.9-27.5 isn't 23.4. Also, why's your average speed in m/s^2 instead of m/s?
 

Related to Calculating Average Speed of Ball in First 5 Seconds

What is the formula for calculating average speed of a ball in the first 5 seconds?

The formula for calculating average speed is distance divided by time. In this case, the distance would be the total distance the ball traveled in the first 5 seconds, and the time would be 5 seconds.

What units should be used for the distance and time measurements when calculating average speed?

The units used for distance and time should be consistent. For example, if the distance is measured in meters, then the time should be measured in seconds. This will give the average speed in meters per second (m/s).

How accurate is the average speed calculation for a ball in the first 5 seconds?

The accuracy of the average speed calculation will depend on the precision of the measurements and the assumptions made in the calculation. For more accurate results, it is important to use precise measurements and make realistic assumptions about the motion of the ball.

What factors can affect the average speed of a ball in the first 5 seconds?

The average speed of a ball can be affected by factors such as air resistance, surface friction, and the force applied to the ball. These factors can cause the ball to accelerate or decelerate, resulting in a different average speed.

How can the average speed of a ball in the first 5 seconds be used in scientific experiments or studies?

The average speed of a ball in the first 5 seconds can be used as a measure of the ball's initial velocity and motion. This information can be used in various experiments or studies involving the motion of objects, such as studying the laws of motion or analyzing the performance of sports equipment.

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