Force, Mass, and Acceleration Practice Problems

1 Name_____Per. _____ Force, Mass, and Acceleration Practice Problems Formulas: Fnet = ma (net Force = mass times Acceleration ) a = v ( Acceleration = change in velocity divided by change in time) t F v Units: Force: Newtons (N) Acceleration : m/sec/sec or m/sec2 velocity: m/sec Conversions: 1 kg = 1000 g m a a t 1 kg weighs ~ 10 N on Earth 1 N = 1 kg-m/sec2 Problems : 1. Two cars accelerate at 2 m/sec2. Car A has a mass of 750 kg, while Car B has a mass of 1000 kg. What forces are required to accelerate each car?

2 If you are concerned with the price of gas, which car would you rather drive and why? 2. A 500 kg rocket can accelerate from rest to a speed of 600 m/sec in 2 seconds. 2a. What is the Acceleration of the rocket? 2b. How much force is required to accelerate it? 2c. How much force would be required to accelerate the rocket if it s mass were twice as much (1000 kg)? Why is payload (the amount of material a rocket carries into space) of extreme importance to rocket scientists? 3. A 100 kg man takes a ride on an elevator. (A) At first it is at rest on the ground floor. (B) It accelerates upward uniformly at 2 m/sec2 for a few seconds, then (C) it continues to go up at a constant velocity of 5 m/sec.

3 3a. Draw and label the forces on the man in during parts A, B, and C of his trip: A. Net Force = _____ B. Net Force = _____ C. Net Force = _____ If the man is standing on a scale (measuring weight in N) in the elevator, what will it read in Part A? _____ Part B? _____ Part C? _____ 3b. Now the man rides down in the elevator. (D) It accelerates downward uniformly at 2 m/sec2 for a few seconds, then (E) the elevator cable breaks and the man goes into freefall. Draw and label the forces on the man in during parts D and E of his trip: D. Net Force = _____ E. Net Force = _____ If the man is standing on a scale (measuring weight in N) in the elevator, what will it read in Part D?

4 _____ Part E? _____ 4. A satellite in space fires its thrusters for 10 seconds to give itself an added velocity of 2 m/sec. Its constant thrusting force is 800 N during this time. What is the mass of the satellite? (Hint: find the Acceleration of the satellite first) 5. A rocket in space has a mass of 5000 kg, and is propelled by a rocket motor with 900,000 N of thrust, which burns for 4 seconds. 5a. What is the rocket s Acceleration ? 5b. If the rocket starts at rest, how fast is the rocket going after the 4 second burn? 6. A 2 kg block is dragged across a table top at a constant velocity by means of a spring scale (force meter) attached horizontally to the block.

5 The scale shows a reading of 4 N at any constant velocity. This means that the frictional force between the block and the table is 4 N, and is not dependent on speed. Draw the forces on the block: Net force = _____ 6b. The block is now pulled with a constant force of 10 N, which accelerates the block across the table top. Draw the forces on the block: Net force = _____ 6c.

6 What is the Acceleration of the block due to this net force? 7. A 75 kg man stands in an elevator. What force does the floor exert on him when the Force Diagrams for man: a. starts moving upward with an Acceleration of m/sec2? b. moves upward with a constant speed of m/sec? c. starts accelerating downward at m/sec2? 8. A boy drops a 5 kg ball off a bridge. Ignoring air resistance, answer the following questions. 8a. Draw a force diagram for the freely falling ball. 8b. What is the net force on the ball? 8c. What is the Acceleration of the ball?

7 8d. How fast is the ball moving after it has been falling for 2 seconds?