# How much force does a 78.0 kg astronaut exert on his chair while sitting at rest on the launch pad?

## Question:

How much force does a 78.0 kg astronaut exert on his chair while sitting at rest on the launch pad?

## Weight:

Weight is not at all similar to mass in any way. In fact, weight calculations require mass. For someone on Earth and at the ground, the weight can be calculated simply by:

{eq}\displaystyle W = mg {/eq}

where:

• m is the mass
• {eq}\displaystyle g = 9.8\ m/s^2 {/eq} is the gravitational acceleration on Earth

Given:

• {eq}\displaystyle m = 78\ kg {/eq} is the mass of the astronaut

When the astronaut is sitting on his chair, there are two forces at work here. The first is the downward weight of the astronaut, which is the force being exerted on his chair and also what we are looking for. The second force is the normal force exerted by the chair on the astronaut, which is equal but opposite. So if we want just the weight, we calculate:

{eq}\displaystyle W = mg {/eq}

We substitute:

{eq}\displaystyle W = (78\ kg)(9.8\ m/s^2) {/eq}

We will get:

{eq}\displaystyle \boxed{W = 764.4\ N} {/eq} 