Divers in Acapulco dive from a cliff that is 65 m high. If the rocks below the cliff extend outward for 25 m, how fast must the diver be
going when he jumps if he just barely clears the rocks? Provide evidence.

Cool question! First step is to find the time taken to fall

57

m

, then to find the horizontal velocity needed to cover

24

m

in that time. In this case the answer is

7.0

m

s

−

1

.

Explanation:

This is a less typical projectile motion question, but it's still projectile motion. This means the horizontal and vertical directions can be considered separately. We assume that the initial vertical velocity,

u

y

=

0

m

s

−

1

, and we are trying to find the required initial horizontal velocity,

u

x

.

To find the time taken to fall

57

m

:

s

=

u

t

+

1

2

a

t

2

Since

u

=

0

, we can rearrange this to:

t

=

√

2

s

a

=

√

2

⋅

57

9.8

=

3.41

s

The horizontal velocity will be constant (ignoring air resistance), so to cover

24

m

in

3.41

s

will be given by:

v

=

s

t

→

u

x

=

24

3.41

=

7.0

m

s

−

1

Answer link

work: w = fd (given)

work done by chet   =50*1 = 50 j

work done by mika =40*2 = 80 j

work done by sara =30*1.5 = 45 j

work done by bill =60*0.5 = 30 j

students in order from the greatest amount of work done to the least is mika> chet> sara> bill

hence option (b) is correct.

i believe the answer would be:

d. violin, clarinet, french horn, and tuba