Steve is driving down a street at 55.0 km/hr. Suddendly a child runs into the street. If it takes steve 0.75 s to react and apply brakes, how many meters will he have moved before he begins to slow down.

This means that

→

v

=

Δ

x

Δ

t

. We can manipulate t

→

v

⋅

Δ

t

Before we put our values into the equation, we will convert the speed to

m

s

55

k

m

h

r

⋅

1000

m

1

k

m

⋅

1

h

r

3600

s

=

15.28

m

s

Now we can calculate

Δ

x

:

Δ

x

=

(

15.28

m

s

)

⋅

(

0.75

s

)

=

11.46

m

∴

You will have moved

11.46

m

before you begin to slow down.

You could also start with the kinematic equation

Δ

x

=

→

v

i

Δ

t

+

1

2

→

a

Δ

t

2

, where

→

a

=

0

. This gives

Δ

x

=

→

v

i

Δ

t

which piece of furniture will have the most inertia and give the furniture movers the most difficulty in moving?  

answer

a 75kg dining table