Projectile Motion Questions: Solving for Time and Velocity

In summary, the conversation discusses attempts to find the time interval between flashes of a stroboscope in a photo of a ball falling freely. The first part involves calculating the distance between the first and second image, then multiplying by a factor of five due to the scale. The second part involves using the equation of motion to find the time interval, with a mistake being made in assuming the time to be 1 second and the initial velocity to be 0 ms(-1). The conversation also discusses the possibility of finding the displacement rather than the time interval between flashes.
  • #1
liquidblot
5
0
Q1

A kangaroo was seen to jump to a vertical height of 2.8m. for how long was it in the air?

Attempt on the solution

not possible? what do you guys think?

Q2

A ball was photographed stroboscopically as it was released and fell freely. eight images appear on the phto which is reduced in scale by a factor of five. use the fact that the acceleration of the ball is 9.8ms(-2) to discover the time interval between the flashes of the stroboscope.


Attempt on the solution

part 1. calculating the distance between the first and second image, then mutiply by 5 (due to the scale factor).

since we are taking the first and second image, it would have a overall time of 1s.

Part 2.
take the calculated length as 0.04m:

v=d/t

v= 0.04/1
= 0.04 ms(-1)

then i got stuck on this step...
 
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  • #2
liquidblot said:
Q1

A kangaroo was seen to jump to a vertical height of 2.8m. for how long was it in the air?

Attempt on the solution

not possible? what do you guys think?

If you drop an object from 2.8m, how log will it take before it hits the ground?

If you can find that, then double it, because the time it took for the kangaroo to reach 2.8m is the same as the time it takes for something to fall that distance, assuming air resistance is neglected.
 
  • #3
liquidblot said:
since we are taking the first and second image, it would have a overall time of 1s.


I don't know how did you find 1s.If the distance between them is 1s,then it must be the time interval between slashes of stroboscope.

liquidblot said:
Part 2.
take the calculated length as 0.04m:

v=d/t

v= 0.04/1
= 0.04 ms(-1)

then i got stuck on this step...

If d=0.04 m is true,

the equation of motion is

[tex]y=vt-\frac{1}{2}gt^2[/tex]

so the distance between slashes should be

[tex]\Delta y=\Delta vt+v\Delta t-gt\Delta t[/tex]

[tex]\Delta v=g\Delta t[/tex]

[tex]\Delta y=gt\Delta t[/tex]

No need to calculate velocity.Note that velocity is not uniform.
 
  • #4
@Bill Foster
oh now i get it, so i have to use of the SUVAT equations to find the time, am i right? (^^)

@azatkgz

i think i had a mistake to take the time as 1s. and also, wouldn't i be taking the initial velocity (u) as 0 ms(-1) because the starting velocity is 0??.

and also, did i mistake the question to find the time interval between the flashes of the stroboscope to be a question on the time taken to reach from 1 image to another?

or is it surpose to mean that i have to find the displacement?
 

1. What is a projectile?

A projectile is an object that is launched or thrown and then moves through the air, influenced by gravity and air resistance.

2. What is the equation for projectile motion?

The equation for projectile motion is: y = y0 + v0yt - 1/2gt2, where y is the vertical position, y0 is the initial vertical position, v0y is the initial vertical velocity, t is time, and g is the acceleration due to gravity.

3. How does air resistance affect projectile motion?

Air resistance, also known as air drag, is a force that acts opposite to the direction of motion. This force can slow down a projectile and affect its trajectory, making it deviate from the expected path.

4. What factors affect the range of a projectile?

The range of a projectile is affected by its initial velocity, angle of launch, air resistance, and the acceleration due to gravity. Other factors such as wind and air density can also have an impact on the range.

5. How is projectile motion used in real life?

Projectile motion is used in many real-life applications, such as sports like basketball and football, where players need to calculate the trajectory of the ball for accurate shots. It is also used in military operations, engineering designs, and even in amusement park rides.

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