Momentum - need serious help :/ (1 Viewer)

[Divided_By_Zero]

I get everything else OK just not momentum:


The question says: A model of a 60kg man and one of a 25kg child were place into a 1000kg car and secured with seatbelts. The car was moving at 70kph (19.444ms^-1) as it was crashed into a brick wall.

a) If the collision took 0.2 seconds. calculate the average force exerted on each model by its seatbelt.

Prelim test for it is in 2 days, need help please!

 

[Drongoski]

I get everything else OK just not momentum:


The question says: A model of a 60kg man and one of a 25kg child were place into a 1000kg car and secured with seatbelts. The car was moving at 70kph (19.444ms^-1) as it was crashed into a brick wall.

a) If the collision took 0.2 seconds. calculate the average force exerted on each model by its seatbelt.

Prelim test for it is in 2 days, need help please!

Isn't force = rate of change of momentum ?? i.e. divide change in momentum (mv) by time (0.2 sec)

 

[Uncle]

p = mv

∑F = m∆p/∆t

so yes that and being a mathematician cunt alone isnt going to help, some 3 unit maths fags just dont understand the physics behind some physical equations.

Back to the question,
Sum of all forces, Newton's Second Law.

∑F = ma

it also means

∑F = m∆v/∆t



∑F = m(v_f-v_i)/∆t

They lolcrashed into a wall hence the final velocity is zero.

∑F = m(0 - v_i)/∆t

Now it's time to sub in the variables, it happened over 0.2 seconds so ∆t = 0.2 and the initial speed v_i you gave was 19.444 m.s^-1

What you want is the force exerted on them, and there seems to be no external forces you mentioned so the equation becomes:

F = - mv_i/∆t

Know

∆t = 0.2
v_i = 19.444 m.s^-1
m = 60kg or 25kg

Don't know

F = ?

That means,
find F when m = 60kg and m = 25kg

 

[Divided_By_Zero]

Cheers but i already figured it out.