A level maths help

mitostudent

I'm really stuck on how to approach this sort of question

Original post by mitostudent

As with standard suvat questions, write down the variables you know and the ones you want to find. With simple questions you know 3 values and want to find the fourth and use a single equation which relates those 4 variables together. Here you need to use two simultaneous equations. Have a go at writing those down and solving for the variable(s).

Reply 3

mitostudent

I've gotten to 10 = 2.1x - 0.5*a*(2.1)^2 and 10 = 1.1x + 0.5*a*(1.1)^2 for both parts respectively using suvat equations. am I on the right track?

Reply 4

mitostudent

I think I've made a mistake

Reply 5

mqb2766

Original post by mitostudent

I've gotten to 10 = 2.1x - 0.5*a*(2.1)^2 and 10 = 1.1x + 0.5*a*(1.1)^2 for both parts respectively using suvat equations. am I on the right track?

The "u" (initial velocity) for the second phase is not the same as the "u" at the start/first phase. In fact, the initial velocity for the second phase is the final velocity from the first phase. So you can use v=u+at on the first phase to get the second phase initial velocity and solve for a (and u).

Or you could use the fact that first+second phase is 20 m in 3.2 s and use that as your second equation and then both equations would have the same initial velocity.

Reply 6

mitostudent

Original post by mqb2766

The "u" (initial velocity) for the second phase is not the same as the "u" at the start/first phase. In fact, the initial velocity for the second phase is the final velocity from the first phase. So you can use v=u+at on the first phase to get the second phase initial velocity and solve for a (and u).
Or you could use the fact that first+second phase is 20 m in 3.2 s and use that as your second equation and then both equations would have the same initial velocity.

for the first equation I used s = 10 , u=u, a=a and t = 2.1 and for the second the same except s = 20 and t = 3.2. I use s = ut + 0.5 at^2 . I get u = 2.43 but the correct answer is 1.92

Reply 7

mqb2766

Original post by mitostudent

for the first equation I used s = 10 , u=u, a=a and t = 2.1 and for the second the same except s = 20 and t = 3.2. I use s = ut + 0.5 at^2 . I get u = 2.43 but the correct answer is 1.92

I get 1.92 so you must have made a mistake solving them. Upload your working if you need to.

Reply 8

mitostudent

Original post by mqb2766

I get 1.92 so you must have made a mistake solving them. Upload your working if you need to.

Thanks I finally figured it out! Sorry for the trouble, I think it was an input error after all

Reply 9

mqb2766

Original post by mitostudent

Thanks I finally figured it out! Sorry for the trouble, I think it was an input error after all

Not sure exactly what you did, but in this case it wasnt after an exact answer, so simply writing the 2 linear simultaneous equations to ~3dp, should have meant it was relatively easy to solve. Similarly, once you had an answer for u and a, you can sub them back into the two equations to verify.

But its good youre sorted.