Question

Instantaneous speed can be negative?

Answer 1

Yes, it just means that the object is slowing down.

Answer 2

I got -96 as answer it can be right?

Answer 3

what is the question.

Answer 4

In physics it is shown that the height of a ball thrown straight up with an initial speed of 96 ft/sec from ground level is S(t)=-16t^2+96t where t is the elapsed time that the ball in the air.

Answer 5

g.what is the instantaneous speed of the ball when it strikes the
ground

Answer 6

I got -96.Is it right?

Answer 7

what t value did u get?

Answer 8

6

Answer 9

t=6

Answer 10

your t is wrong

Answer 11

the answer should be -19

Answer 12

-16t^2+96t=0
16t(t-6)=0
16t=0
t=0
t-6=0
t=6
t=0,6

Answer 13

oh sorry, i read 19 instead of 96

Answer 14

-96 is correct.

Answer 15

-32t+96 where t=6

Answer 16

so it can be negative?

Answer 17

yes

Answer 18

thanks for the help

Answer 19

np

Answer 20

anything else?

Answer 21

I have a doubt

Answer 22

acceleration can be negative?

Answer 23

yes

Answer 24

thanks for the help

Answer 25

np

Answer 26

speed is |velocity|

Answer 27

you found velocity

Answer 28

just one step further to find speed

Answer 29

in other words speed is always positive or ( I guess you can say ) zero (if an object is going anywhere)

Answer 30

@arjund12
-ve speed does NOT mean that he object is slowing down (you are confusing it with acceleration).

@sammy12
Strictly speaking SPEED cannot be negative, because it is a scalar property.

Velocity is a property which is speed AND direction.

Therefore, once you have defined which way is 'positive' for your distance measurement then velocity is also defined as positive in the same direction.

In your case you are strictly talking about velocity (since it changes from upwards to downwards motion) and hence it can be -ve (In your case the height (i.e. distance) is measured as positive in an upwards direction, so if the ball is travelling downwards then its velocity is negative.)

Answer 31

oops just notice
I meant to say nowhere above when talking about speed being zero :p
but I guess everyone figured that