Question

A rocket takes off from Earth's surface, accelerating straight up at 47.2 m/s2. Calculate the normal force (in N) acting on an astronaut of mass 89.4 kg, including his space suit. (Assume the rocket's initial motion parallel to the +y-direction. Indicate the direction with the sign of your answer.)

Answer 1

The normal force acting on the astronaut is equal to the astronaut's weight minus the force of gravity acting on him. The force of gravity acting on the astronaut is equal to his mass times the acceleration due to gravity on Earth (9.8 m/s^2).

F_norm = F_gravity - ma = (89.4 kg)(9.8 m/s^2) - (89.4 kg)(47.2 m/s^2) = -4095.56 N

In this case the direction of the force is opposite to the direction of the acceleration. So the force is acting in -y direction. So the answer is -4095.56 N.