Notes, February 17, 2011

Notes: February 17, 2011From the Force Diagrams and Net Force worksheet:

1. An elevator is moving up at a constant velocity of 2.5 m/s. The passenger has a mass of 85 kg.
a) Force diagram of the passenger:

b) Calculate the force the floor exerts on the passenger: (85 kg) x (10N / 1 kg) = 850 N

2. The elevator accelerates upwards at 2.0m/s^2
a) Force diagram of the passenger:
b) Equation for the vertical force on the passenger: Force unbalanced = (acceleration) x (mass)
c) Calculate the force the floor exerts on the passenger:Force unbalanced = (2.0 m/s ^2) x (85 kg)Force unbalanced = 170 NForce unbalanced + Normal force = vertical forceVertical force = 170 N + 850 NVertical force = 1020 N

3. The elevator accelerates downward at 3.0m/s^2
a) Force diagram of the passenger:

b) Write the equation for the vertical forces on the passenger: Force unbalanced = (acceleration) x (mass)
c) Calculate the force the floor exerts on the passenger:( 85 kg) x (10 N / 1 kg) = 850 N

4. While descending in the elevator, the cable breaks. How big is the force on the passenger by the floor?
a) At the moment that the cable breaks, the passenger and elevator accelerate downward at 9.8 m/s ^2.
b) Afterwards, the force of the floor on the passenger would be zero.
c) Relative to the elevator, the passenger would be weightless.

5. A 70 kg skydiver jumps out of an airplane. Immediately after jumping, how large is the skydiver’s acceleration?
a) Acceleration due to earth’s gravity = 9.8 m/s ^2
b) Upon reaching a downwards velocity of 100 miles per hour, 300 N of drag resist the diver’s motion. Draw a force diagram and calculate how large is the skydiver’s acceleration.
Force unbalanced = (acceleration) x (mass)
Acceleration = (Force unbalanced) / (mass)
Acceleration = (700 N – 300 N) / 70 kg
Acceleration = 400 N / 70 kg
Acceleration = 5.71 m/s ^2

6. A 900 kg car that exerts 5000 N of traction force on a level road while being opposed by 1000 N of friction and drag forces (combined)
a) Force diagram of car:
b) Write a net force equation for the car:
Force unbalanced = (acceleration) x (mass)
c) Calculate the acceleration of the car: Acceleration = (Force unbalanced) / (mass)
Acceleration = (5000 N – 1000 N) / (900 kg)
Acceleration = 4000 N / 900 kg
Acceleration = 4.44 m/s ^2