After ten years of a two-hour commute, Brenda has gotten sick and tire of it. So

Question

After ten years of a two-hour commute, Brenda has gotten sick and tire of it. So she bought a rocket pack. (The mass of Brenda and her rocket pack is 70.0 kg.

Answer the three questions below using three significant figures. (Let g = 9.81 m/s2.)

Part A: How much upward force must the rocket provide in order for Brenda to hover motionless in the air?

Part B: If the upward force from the rocket were equal to FR = 1030 N, what is Brenda's upward accleratin?

Part C: In order to be safe when she is landing at the end of her commute, her downward acceleration must be a = -0.400 m/s2. How much thrust doest the rocket need to supply in order to achieve such an acceleration.

Explanation / Answer

Here,

part A)

total mass ,m = 70 kg

for brenda to remain motionless in air

net force on Brenda must be zero

Upwards force = 70 * 9.8

Upwards force = 686 N

the Upwards force needed is 686 N

part B)

let the acceleration is a

using second law of motion

Fnet - F = m * a

1030 - 686 = 70 * a

a = 4.914 m/s^2

the acceleration of the rocket is 4.914 m/s^2

part B)

let the thrust force is F

F - mg = m * a

F - 70 * 9.8 = -70 * 0.40

F = 658 N

the thrust force needed is 658 N

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