How Do You Solve Rectilinear Motion Problems with Missing Data?

[Sebc]

Hi, I recently stumbled across your forums whilst trying to find help for my homework. I have managed to do all the questions on the homework except these 2, and i cannot seem to get the right answers to them. This is because they both miss one piece of data and i would normally use the suvat equations to find the answer.

Homework Statement

A body moving with uniform acceleration covers 64.4m in 7 seconds. And 110m in 10 seconds.

Find acceleration and initial velocity.

Homework Equations

Suvat / equations of motion

The Attempt at a Solution

(110 - 64.4 ) / (10- 3)

The only other thing i could think of would be adding them and trying to work it out.. but as i don't know the start velocity i cant. ( 174.4 / 17)Question 2

Homework Statement

A body released from rest falls through 44.1m during the fifth second of its motion find the acceleration due to gravity.

u= 0, s(5) - s (4) = 44.1m

Sorry there's not much working out from me, I am just new to physics (started it about a month ago) and asides from filling in data into the suvat equations i really have no idea what I am doing. could somebody point me in the right direction , thankyou

 

[learningphysics]

For both problems, the equation you need is:

d = v1*t + (1/2)at^2

for the first problem... plug in your 2 sets of values... d = 64.4 t=7 and d= 110 t= 10

2 equations... 2 unknowns... you can solve both v1 and a.

For the second problem, again try to use

d = v1*t + (1/2)at^2

 

[Sebc]

For both problems, the equation you need is:

d = v1*t + (1/2)at^2

for the first problem... plug in your 2 sets of values... d = 64.4 t=7 and d= 110 t= 10

2 equations... 2 unknowns... you can solve both v1 and a.

For the second problem, again try to use

d = v1*t + (1/2)at^2

Is the equation not d= v*t - (1/2) at^2?Because i used that and got 12.6 = 59.5a So a = 0.2 But the answer says a = 1.2

But thanks for your help, maybe i did it wrong ill try againEDIT EDIT EDIT: WEWT. Ignore me i did a calculation wrong. :) Now all i got to do is solve the second one

ty btw i didnt realize i could just turn it into simultaneous equations