Question

A 35.0 kg dolphin decelerates from 12.0 to 7.50 m/s in 2.30s to join another dolphin in play. What average force was exerted to slow him if he was moving horizontally? (The gravitational force is balanced by the buoyant force of the water)

Answer 1

first answer these questions:

1) What is the total change in velocity
2) What is the time it takes to change (Ans= 2.3s)
3) What is the average change per second

The answer to 3 gives you the average acceleration

NOW:
Force = m x a

and you know the mass and you know the acceleration

so you can calculate the force

Answer 2

Force =(mass)(acceleration)
F = (35.0kg)(2.3s)
F = 80.5
is that right?

Answer 3

no

answer the 3 questions first - you need to calculate the acceleration from those questions....

Answer 4

you wrote

Force =(mass)(acceleration) - this is correct
F = (35.0kg)(2.3s)

Answer 5

Force =(mass)(acceleration)
F = (35.0kg)(2.3s) - THIS is (mass)(time)

you need to work out acceleration first

Answer 6

acceleration = rate of change of velocity

in this case

average acceleration = change of velocity /2.3s

Answer 7

a = V-Vo/ t
a = 7.50m/s - 12.0m/s / 2.30s
a = -1.957m/s^2
is that right?

Answer 8

yes

Now you can use
F=ma to work out the average F

Answer 9

f = (35.0kg)(-1.957)
f = -68.495
is it right?

Answer 10

Yes - but you should always include units

if Mass is in kg and a is in ms^-2 then what is the unit of Force?

Answer 11

-68.495Newton's

Answer 12

OK - good

Answer 13

Thanks MrNood. I really appreciate your help.

Answer 14

np