To calculate the acceleration of a 70-kg mass on a swing if you push it with a 40-N force, you can use Newton's second law of motion, which states that the acceleration of an object is directly proportional to the net force applied to it and inversely proportional to its mass.

The formula for Newton's second law is:

```

F = ma

```

Where:

- F is the net force applied to the object (in Newtons)

- m is the mass of the object (in kilograms)

- a is the acceleration of the object (in meters per second squared)

In this case, the net force applied to the object is 40 N, and the mass of the object is 70 kg. So, the acceleration of the object can be calculated as follows:

```

a = F/m = 40 N / 70 kg = 0.57 m/s²

```

Therefore, the acceleration of the 70-kg mass on the swing is 0.57 m/s².