Example from Physics, 4.3 Newton's Second Law of Motion

What Acceleration Can a Person Produce when Pushing a Lawn Mower?

Suppose that the net external force (push minus friction) exerted on a lawn mower is 51 N parallel to the ground. The mass of the mower is 240 kg. What is its acceleration?

A man is facing to the right and is pushing a lawn mover forward. The force exerted on the lawn mower is labeled with a right-facing vector, F net.

Figure 4.6

Work it out on paper first. Then open the solution one step at a time, and stop as soon as you can finish on your own.

Strategy
Because F_net and m are given, the acceleration can be calculated directly from Newton’s second law: F_net = ma.
Solution
Solving Newton’s second law for the acceleration, we find that the magnitude of the acceleration, a, is $a = \frac{F_{net}}{m} .$ Entering the given values for net external force and mass gives
$a = \frac{51 N}{240 kg}$
4.9

Inserting the units $kg \cdot {m/s}^{2}$ for N yields
$a = \frac{51 kg \cdot {m/s}^{2}}{240 kg} = 0.21 {m/s}^{2} .$
4.10

0 of 2 steps open

How did it go?

Strategy

Solution

Strategy

Solution