Question

A 1.50 x 10^3 kg car leaves a parking lot. Thirty seconds later it is moving along a highway at 72km/hr.

a. What is the car's change in momentum
b. What average force does the motor produce to bring about this change in momentum.

Answer 1

What is the definition of momentuM?

Answer 2

Isn't it the movement of an object through intertia?

Answer 3

What is the true definition?

Answer 4

72 km/hr = 20 m/s
change in momentum = final momentum - initial momentum
= (1.5E3) (20) - 0 = 30,000 kg m/s

force = mass * acceleration

acceleration = (20m/s)/30s = 2/3 m/s^2

force = (1.5E3) (2/3) = 1000 N

Answer 5

isn't it p72km/h−pparked=Δp

Answer 6

yes, that's what i did. I just changed the unit to m/s

Answer 7

i get 108000?

Answer 8

1.5x10^3(72)-1.5x10^3(0) = 108000

Answer 9

well, that's correct if you don't want to change to m/s.
108,000 kg km/hr = 30,000 kg m/s

Answer 10

okay now I understand. Also how would we achieve b?

Answer 11

find acceleration, and use F = ma

Answer 12

how do we find acceleration?

Answer 13

Is there a specific formula?

Answer 14

acceleration = (final velocity - initial velocity)/time

Answer 15

so then. Its 72-0/30

Answer 16

and then p=mv

Answer 17

well the unit will be different. (km/hr)/s is isn't too conventional. it better to convert to (m/s)/s

Answer 18

i mean 3600kmhr/s