Physics help - velocity time graph

A tennis ball is thrown vertically downwards and bounces on the ground. The ball leaves
the hand with an initial speed of 1.5 m s–1 at a height of 0.65 m above the ground. The
ball rebounds and is caught when travelling upwards with a speed of 1.0 m s–1.
Assume that air resistance is negligible.
Show that the speed of the ball is about 4 m s–1
Done this part.
The ball is released at time t = 0. It hits the ground at time tA and is caught at time tB.
On Figure 1, sketch a velocity–time graph for the vertical motion of the tennis ball from
when it leaves the hand to when it returns. The initial velocity X and final velocity Y are
marked on Figure 1.
Heres the picture of the markscheme answer:

My question is: Why is the velocity at A, 3 ms-1? I dont understand where they got that from!?

(edited 7 years ago)

OP

Bump!
@samb1234

Original post by Someboady

Bump!
@samb1234

What does the gradient represent and how can you use that to help us (hint: think about what is already given in the question)

Reply 3

Someboady

OP

17

Original post by samb1234

What does the gradient represent and how can you use that to help us (hint: think about what is already given in the question)

Ah got it. So I can draw the first part of the graph and then use the gradient of that and draw the line back, to tA which would lead me to it being 3ms-1.
This kinda stumped me xD, I tried to use suvat to figure it out. How did you know immediately to use the gradient?

Reply 4

samb1234

13

Original post by Someboady

Ah got it. So I can draw the first part of the graph and then use the gradient of that and draw the line back, to tA which would lead me to it being 3ms-1.
This kinda stumped me xD, I tried to use suvat to figure it out. How did you know immediately to use the gradient?

Intuition i guess, but them plotting the final point is a massive giveaway, and then it just makes sense that the gradient should be the same for both as gradient =g which is the same for both

Reply 5

Someboady

OP

17

Original post by samb1234

Intuition i guess, but them plotting the final point is a massive giveaway, and then it just makes sense that the gradient should be the same for both as gradient =g which is the same for both

Ah okay! Thanks again!
There's this one topic im kind of stuck on. Its to do with waves and path differene
I've seen two questions (one on the new specimen paper) and one on a really old unit 10 paper. It basically asks you to find a distance by using the path difference. So you calculate the path difference and find the distance. In both questions the path difference = 2 * the distance (in context) and I don't understand where this comes from.
Heres the old one: (part ii)

Reply 6

samb1234

13

Original post by Someboady

Ah okay! Thanks again!
There's this one topic im kind of stuck on. Its to do with waves and path differene
I've seen two questions (one on the new specimen paper) and one on a really old unit 10 paper. It basically asks you to find a distance by using the path difference. So you calculate the path difference and find the distance. In both questions the path difference = 2 * the distance (in context) and I don't understand where this comes from.
Heres the old one: (part ii)

Sorry i havent done waves for a year so probably best to make a thread asking about it