Question

A person takes 2 seconds to reach his maximum speed of 18km/hr.What is the magnitude of average acceleration?

Answer 1

oh k wait please

Answer 2

a = (v-u)/t = 5 / 2 ms^{-2}

Answer 3

\[\large{\frac{v-u}{t}=a}\]
\[\large{\frac{5}{2}ms^{-2} =a}\]

Answer 4

what is u?

Answer 5

Initial speed = u

Answer 6

v= final speed

Answer 7

i mean the value of u!!

Answer 8

how did you get v-u as 5?

Answer 9

since u = 0 m/s
and v = 18 km/hr = 18 * 5/18 m/s = 5 m/s

Answer 10

why is u 0?

Answer 11

nowhere mentioned,you cant do that

Answer 12

hmn.. wait then

Answer 13

he was already at some initial speed and then then finally he speeded up to 5m/s

Answer 14

options given?

Answer 15

answer is 2.5m/s^2

Answer 16

check the question again @DLS

Answer 17

its correct but..

Answer 18

i did

Answer 19

the process I did is wrong since u is not equal to 0

Answer 20

yes

Answer 21

Average acceleration is defined as:\[a_{avg}=\frac{\Delta v}{\Delta t}=\frac{v_f-v_i}{t_f-t_i}\]We have no choice to assume that the initial velocity is 0, and the rest of the information is given in the problem, so\[a_{avg}=\frac{18\frac{km}{hr}-0\frac{km}{hr}}{2s-0s}=\frac{18 \frac{km}{hr}}{2s} \times \frac{1hr}{3600s} \times \frac{1000m}{1km}=2.5\frac{m}{s^2}\]

Answer 22

@Xishem also took u = 0 ..

Answer 23

that's it..

Answer 24

NO CHOICE ... other than to assume u = 0 m/s

Answer 25

You have to assume that the initial velocity is 0 since there is no initial velocity given. Average acceleration is dependent on knowing initial velocity beforehand.

Answer 26

just how can we assume lol

Answer 27

its just not possible

Answer 28

logically

Answer 29

lol then quest. is wrong @DLS until we r given with u = 0 km/h or 0 m/s

Answer 30

You have to make an assumption because you have no other choice. Given the context of the question, it is either impossible to answer, or you have to make an assumption that v_i is 0.

Answer 31

right @Xishem

Answer 32

okay..

Answer 33

sorry ...

Answer 34

thanks

Answer 35

no problem though

Answer 36

Any other question I've seen similar to this starts off something like "An object initially at rest...".

The wording of this question is just bad.

Answer 37

right..

initially at rest means u = 0 m/s