• We need your support!

    We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
    Click here to Donate Now (View Announcement)

Physics: Post your doubts here!

Messages
121
Reaction score
32
Points
38
I'll post the answers. You'll be surprised just as I was.

a. horizontal velocity= s/t = 2.5/0.6= 4.17m/s

b. Vertically final velocity is zero as ball passes over cross-bar.
v = u + at
0 = u - (9.81*0.6)
u = 5.89m/s (ans)

c. u = root over(4.17^2 + 5.89^2)
= 7.21m/s

d. angle = tan^-1 (5.89/4.17)
= 55degrees

The mark scheme totally trolled me!!! I don't get it. How can horizontal velocity be 2.5/0.6 ??
 
Messages
121
Reaction score
32
Points
38
An athlete bends down and then jumps straight up into the air. At the instant he starts his jump
three forces act on him – his weight, an upthrust from the air and the contact force with the
ground. What is the correct order in increasing magnitude of these three forces
A. contact force weight upthrust

B. upthrust contact force weight

C. upthrust weight contact force
D. weight upthrust contact force

Provide an explanation if you can answer. It's not from past papers.
 
Messages
844
Reaction score
2,495
Points
253
I'll post the answers. You'll be surprised just as I was.

a. horizontal velocity= s/t = 2.5/0.6= 4.17m/s

b. Vertically final velocity is zero as ball passes over cross-bar.
v = u + at
0 = u - (9.81*0.6)
u = 5.89m/s (ans)

c. u = root over(4.17^2 + 5.89^2)
= 7.21m/s

d. angle = tan^-1 (5.89/4.17)
= 55degrees

The mark scheme totally trolled me!!! I don't get it. How can horizontal velocity be 2.5/0.6 ??


2.5m was the vertical distance. There's no way it can be used to calculate the horizontal distance. the two components are perpendicular.
I don't get how this is possible. :confused:
 
Messages
958
Reaction score
3,499
Points
253
okay i think this is simple but am kinda confused::cry:

3bii.) - i don't get why to calculate the time only the vertical distance is considered
3biii.) - why do we use the horizontal velocity to calculate the speed.....and the time is the same as the journey of the ball before colliding with the wall??:confused:

Question paper: http://www.xtremepapers.com/papers/...nd AS Level/Physics (9702)/9702_w11_qp_21.pdf
Marking scheme:http://www.xtremepapers.com/papers/...nd AS Level/Physics (9702)/9702_w11_ms_21.pdf

please help urgently:( thanx so much.....May God bless you
 
Messages
958
Reaction score
3,499
Points
253
reposting my question....please helppppp

okay i think this is simple but am kinda confused::cry:

3bii.) - i don't get why to calculate the time only the vertical distance is considered
3biii.) - why do we use the horizontal velocity to calculate the speed.....and the time is the same as the journey of the ball before colliding with the wall??:confused:

Question paper: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w11_qp_21.pdf
Marking scheme:http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w11_ms_21.pdf

please help urgently:( thanx so much.....May God bless you
 
Messages
229
Reaction score
41
Points
38
:) since the ball's initial velocity after collision is perfectly horizontal, take the horizontal distance moved and divide it by the time above(1.333)
horizontal velocty stays constant throughout travel.
 
Messages
121
Reaction score
32
Points
38
3.b.i v^2=u^2 - 2gs
--> 0= 13^2 - (2*9.81 s)
--> s= 8.61 ~ 8.61m
3.b.ii v= u -gt Alternatively, you can also use horizontal velocity to calculate the time.
--> 0= 13 - 9.81*t time = distance/ horizontal velocity = 9.95/7.5 = 1.33 s
--> t= 1.325 s ~ 1.33 s

3. b.iii using vertical velocity, The horizontal velocity IS THE SPEED after rebounding from P. There is no vertical speed at P since in the beginning of the question
--> s= ut + .5 gt^2 it was said "The ball hits the wall at P with a velocity that is at right angles to the wall" This means there is no vertical velocity at P.
--> 8.61 = 4.905 t^2
--> t = 1.324 s

so horizontal velocity = 6.15/1.324 = 4.64 ~ 4.6 m/s

Hope that helps. :)
 
Messages
958
Reaction score
3,499
Points
253
3.b.i v^2=u^2 - 2gs
--> 0= 13^2 - (2*9.81 s)
--> s= 8.61 ~ 8.61m
3.b.ii v= u -gt Alternatively, you can also use horizontal velocity to calculate the time.
--> 0= 13 - 9.81*t time = distance/ horizontal velocity = 9.95/7.5 = 1.33 s
--> t= 1.325 s ~ 1.33 s

3. b.iii using vertical velocity, The horizontal velocity IS THE SPEED after rebounding from P. There is no vertical speed at P since in the beginning of the question
--> s= ut + .5 gt^2 it was said "The ball hits the wall at P with a velocity that is at right angles to the wall" This means there is no vertical velocity at P.
--> 8.61 = 4.905 t^2
--> t = 1.324 s

so horizontal velocity = 6.15/1.324 = 4.64 ~ 4.6 m/s

Hope that helps man. :)
tx soooooo much!!!! God bless:)
 
Messages
121
Reaction score
32
Points
38
An athlete bends down and then jumps straight up into the air. At the instant he starts his jump
three forces act on him – his weight, an upthrust from the air and the contact force with the
ground. What is the correct order in increasing magnitude of these three forces
A. contact force weight upthrust

B. upthrust contact force weight

C. upthrust weight contact force
D. weight upthrust contact force

Provide an explanation if you can answer. It's not from past papers.
 
Top