a 2150kg truck is travelling along a straight road at a constant speed of 55km/h when the driver removes his foot from the gas. After 21s the trucks speed is 33km/h. What is the magnitude of the average net force acting on the truck during the 21s interval.
626N
1890N
972N
2250N
229N

Question

a 2150kg truck is travelling along a straight road at a constant speed of 55km/h when the driver removes his foot from the gas. After 21s the trucks speed is 33km/h. What is the magnitude of the average net force acting on the truck during the 21s interval.
626N
1890N
972N
2250N
229N

snowsurf · Answer

You use the same equations like in the previous problem except you go backwards. You find acceleration then you can find the force since you know the mass of the truck.

anonymous · Answer

I tried that I did 55(2150)/21 and did not get the right answer

anonymous · Answer

@snowsurf

snowsurf · Answer

Lets work this out together. List me the information you are given.

anonymous · Answer

m=2150kg
vi=55km/h
vf=33km/h
t=21s
@snowsurf

snowsurf · Answer

Great. Now we need an equation that can find us acceleration using the information  you have. There are several kinematic equations but one will work. You need an equation that can related vf, vi and t to get a.

anonymous · Answer

is it the one where v=vo+1/2at ? @snowsurf

snowsurf · Answer

You have it the correct form just remove the 1/2. Then solve for a.

snowsurf · Answer

Also want to mention you have to covert their speed from km/h to m/s

anonymous · Answer

vi-vf/t
=55-33/21
=1.05
But I did that in km/h
@snowsurf

snowsurf · Answer

You can use Google calculator to convert it.

snowsurf · Answer

But you do have the right idea. So use Google to convert and then calculate acceleration a.

anonymous · Answer

OKay I got 6.11113 @snowsurf

snowsurf · Answer

Okay. Great that is your a. So a =6.1, we will round it so we don't have so many 1.
Now you know acceleration and mass of truck. Now what equation allow you to calculate force?

anonymous · Answer

F=ma
=2150x6.1
=13115N
@snowsurf

snowsurf · Answer

Opps I look at the problem it says average force. My bad. This won't give you the answer. This is only for force at a given instant of time. We are given$$\Delta t$$which is average time. The equation that will relate to this is impulse equation.

snowsurf · Answer

$$F _{avg}\Delta t = m \Delta v$$ That is the impulse equation.

snowsurf · Answer

Did you calculate it?

anonymous · Answer

Sorry Open study keeps freezing on me and would the equation be F=mv/t?
F=(2150)(6.1)/21

snowsurf · Answer

That is correct.