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Physics question in ocr textbook (please help)

I attached the full question and the diagram it refers to. I can do (a) and (b) but I have no idea what (c) is asking? please could someone explain to me how I would go about doing that? Thanks! And if you could be extra helpful it would be great if you could go through (d) too? But i don't mind about (d) as much...

also:
The answer to (b) is 44.4m/s , which you get by substituting into the equation Ft=mv-mu

If you can't read the question please let me know and I'll type it out
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Original post by conorconorconor
I attached the full question and the diagram it refers to. I can do (a) and (b) but I have no idea what (c) is asking? please could someone explain to me how I would go about doing that? Thanks! And if you could be extra helpful it would be great if you could go through (d) too? But i don't mind about (d) as much...

also:
The answer to (b) is 44.4m/s , which you get by substituting into the equation Ft=mv-mu

If you can't read the question please let me know and I'll type it out


I think part c is just asking you for the mean force, which is easy enough to work out if you have worked out the final velocity.
Original post by Ollie231213
I think part c is just asking you for the mean force, which is easy enough to work out if you have worked out the final velocity.
Sorry if this is stupid, but ... how would I do that? Sorry I'm just really confused I can't work it out.. :frown:
Original post by conorconorconor
Sorry if this is stupid, but ... how would I do that? Sorry I'm just really confused I can't work it out.. :frown:


I haven't looked at the question in a lot of detail, so I'm not sure if this is right, but since you've found the impulse the ball receives, you can use FΔt=Δ(mv)F\Delta t = \Delta (mv) to find the change in momentum. You know the ball starts from rest, i.e. its initial momentum is 0, so you can find its final momentum. Hence you can find the ball's final velocity, and from that the ball's average acceleration, and finally the mean force acting on the ball.

I think that would work...

Edit: Oh wait, you've already calculated the final velocity in part (b), so scrap the first part of that...
(edited 7 years ago)
Original post by conorconorconor
Sorry if this is stupid, but ... how would I do that? Sorry I'm just really confused I can't work it out.. :frown:


Just rearrange Ft = mv to get F = mv/t :wink:
Original post by Ollie231213
Just rearrange Ft = mv to get F = mv/t :wink:


Thank you so much for helping with this, but I tried this just now;

F = (0.045x44.4)/1.5

and I get around 1.3N but in the back of the book it says the answer is 1200N (although they worked out (b) as 42 instead of 44.4, but still) ... am I doing something wrong or is the answer in the back a typo or something? :s
Original post by conorconorconor
Thank you so much for helping with this, but I tried this just now;

F = (0.045x44.4)/1.5

and I get around 1.3N but in the back of the book it says the answer is 1200N (although they worked out (b) as 42 instead of 44.4, but still) ... am I doing something wrong or is the answer in the back a typo or something? :s


You need to look at the units of the time :smile:

Oh, and the time isn't exactly 1.5, so your answer should give you approximately 1200N
Original post by M0nkey Thunder
You need to look at the units of the time :smile:

Oh, and the time isn't exactly 1.5, so your answer should give you approximately 1200N


OHHHHHHHH wooooooow that explains it all omg :s-smilie:

Thanks everybody for helping me I can go on with my life now without this question haunting me for eternity :smile:

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