Question

When you see a traffic light turn red, you apply the brakes until you come to a stop. Suppose your initial speed was 10.7 m/s, and you come to rest in 34.7 m. How much time does this take? Assume constant deceleration

Answer 1

u = 10.7
v = 0
a = ?
t = ?
s = 34.7 m
v^2 - u^2 = 2as
find a by above eq
then v = u + at
find t by above eq

Answer 2

k?

Answer 3

uhm the answer I found is not correct. So i don't understand what you did there.

Answer 4

i think you multiplied v & u by 2 in 1st eq
you are supposed to square it

Answer 5

no i did square it. My answer for the first equation was -1.65?

Answer 6

yeah thats right
is the time 6.488

Answer 7

i got neg. 9.05 for the time. Can you show me how you got 6.488?

Answer 8

yes

Answer 9

v = u + at
0 = 10.7 -1.65t

Answer 10

so t = \[-10.7\div-1.65 = \]

Answer 11

that is 6.488

Answer 12

k?

Answer 13

okay I see what I did wrong. Thank you !

Answer 14

can you help me with another problem?

Answer 15

yea

Answer 16

fire away

Answer 17

A volcano launches a lava bomb straight upward with an initial speed of 20 m/s. Taking upward to be the positive direction, find the speed and direction of the lava bomb after the following amounts of time have elapsed.

a) 1.0 seconds (speed & velocity in m/s)
b)3.1 seconds (speed & velocity in m/s)

Answer 18

u = 20
a = g(grav) = -9.8
t = 1 , 3.1
find v using v = u + at

Answer 19

thank you ! you are a physics genius !

Answer 20

2*34,7*a=10,7^2 a=1,64 1,64*t=10,7 t=6,48