Basic Force and Acceleration Problems

Basic force and acceleration problems

1.  A 4600 kg helicopter accelerates at 2 m/s2 upward. What is the lifting force exerted by the propellers?

2.  The maximum force that a grocery bag can withstand without ripping is 250N. Suppose the bag is filled with 20kg of groceries and lifted with an acceleration of 5 m/s2. Does the grocery bag rip? How do you know?

3.  A student, standing on a scale in an elevator, sees that his weight on a scale (while the elevator is not moving) is 840 N. As the elevator rises from the ground floor, his apparent weight becomes 1050N. The elevator then begins to slow down as it approaches the 10th floor, and his apparent weight drops to 588N. Determine the magnitude and direction of the acceleration of the student at the beginning and the end of the trip.

4.  A sign in an elevator states that the maximum occupancy is 20 people. Suppose that the engineers assume the mass of the average person is 75 kg. The elevator itself has a mass of 500 kg. The cable supporting the elevator can tolerate a maximum force of 30,000N. What is the greatest rate of acceleration that the elevator’s motor can produce without snapping the cable?

5.  A race car has a mass of 710 kg. It start from rest and travels a distance of 40 meters in 3 seconds. Assuming a uniform acceleration for the car, what is the net force acting on it?

6.  Suppose that a 1000 kg car is traveling at 25 m/s. Its brakes can apply a force of 5000N. What is the minimum distance required for the car to stop?

7.  A 65 kg woman falls into the water from a 10 meter high platform (ignore air resistance).

a.  What is the net force on the woman as she is in the air?

b.  What is her speed as she hits the water?

c.  If she comes to a stop 2 meters below the surface of the water, what net force does she experience?

8.  During a head-on collision, a child in the front seat of a car accelerates from 13.3 m/s to a stop in 0.10 seconds.

a.  What is the acceleration of the child?

The driver of the car holds out her arm to keep the 25 kg child (no seat belt) from hitting the dashboard.

b.  What is the child’s weight?

c.  What force must the driver exert on the child to keep him from hitting the dashboard (a force equal in magnitude to the net force the child would experience)?

d.  Convert the answer to part C from Newtons to pounds (1 lb = 4.45 N). What are the chances the driver will be able to stop the child?