Question

A 1.5 kilogram cart initially moves at 2.0 meters per second. It is brought to rest by a constant net forcé in 3.0 second. What is the magnitude of the net force ?

Answer 1

The net force on the cart is

Force = (mass) x (acceleration) .

We know the mass = 1.5 kilogram, but we need to
calculate the acceleration.

Acceleration = (change in speed) / (time for the change)

Change in speed = (ending speed) minus (beginning speed)

= ( 0 ) - ( 2 m/s ) = -2 m/s

Acceleration = (change in speed) / (time for the change)

= ( -2 m/s ) / (3 sec)

= - 2/3 m/s² .

Finally ... Net force = (mass) x (acceleration)

= (1.5 kilogram) x ( - 2/3 m/s²)

= ( - 3/2 x 2/3 ) (kg-m/s²)

= - 1 newton .

The negative sign on the force means the force is applied
opposite to the direction the cart is moving. That gives
negative acceleration (slowing down), and the cart
eventually stops.