The speed-time graph of a 500g cart changes is shown on the left.
What is the force acting on the cart over the 14 second period?

Step 1 = Change mass into kilograms
500g = 0.5Kg
Step 2 Calculate the acceleration.
acceleration = change in speed/period of time
Change in speed = final speed - initial speed =
40 -10=30m/s
Period of time = 14 seconds
Step 3 Acceleration = 30m/s/14/s = 2.14 m/s/s
The force = 0.5kg X 2.14m/s/s = 1.07 Newtons

Incorrect
Some hints.
The formula you should use is
F =ma

The acceleration is the change in speed over time.
Calculate the acceleration.
The acceleration is the gradient (slope) of the speed-time graph.
(Initial speed - final speed ) / time taken (seconds)=acc.
The mass of the cart is given as 500g.
Change the mass of the cart into kilograms.