Chapter 5 \ Forces \ Problems

1.) When a shot-putter exerts a net force of 140 N, north on a shot, the acceleration
      of the shot is measured to be 19 m/s2, north. What is the mass of the shot?   S

2.) Together, a motorcycle and its rider have a mass of 375 kg. If they are traveling north,
      what net force would be required to cause an acceleration of 4.50 m/s2, south?   S

3.) A truck, mass 1715 kg, travelling west at 120 km/h, slows to a stop in 8.57 seconds.
      What is the magnitude and direction of the net force that acted on the truck?   S

4.) How long must a net force of 796 N, east act on a 1435 kg vehicle
     traveling at 103.5 km/h, west to bring it to rest?   S

5.) Find the displacement of a 4082 kg jet if it is uniformly accelerated
      from rest by a net force of 35.4 kN, south for 17.3 seconds.   S

6.) Find the net force acting on a couch if the applied forces are 327.4 N, west
      and 353.6 N, west while the force of friction is 61.7 N.   Help

7.) Find the net force acting on a box if the applied forces are 653.2 N, north
      and 286.4 N, south while the force of friction is 38 N.   H

8.) A freezer moving across a floor at constant speed has two people moving it.
     One is pushing 186.3 N from behind while the other is pulling 74.5 N from the front.
     What is the force of friction?   H

9.) Find the acceleration of a 12.5 kg object if the applied force is 57.3 N, east
     and the force of friction is 29.73 N.   H

10.) A tree trunk, mass 118.2 kg, is accelerated at 3.75 m/s2, west when pulled by a tractor.
       What is the force of friction if the tractor exerts 500 N, west on the tree trunk?   H

11.) What must the mass of an object be if it accelerates at 1.07 m/s2,
       when the applied force is +562 N and force of friction is 145.8 N   H

12.) Starting from rest, a 455 kg motorcycle and rider reaches a velocity of 100.0 km/h, east
       in 5.31 seconds. Find the necessary applied force if the friction force is 84.6 N.   H

13.) Initially at rest, a 9.73 kg box reaches a velocity of + 3.72 m/s at a position + 2.64 m
       from its starting point. If the applied force is + 29.25 N, find the force of friction.   H

14.) Find the force of gravity on the following masses:
       a) exactly twenty kilograms        b) 101.5 kg football player        c) 65 g chocolate bar   H

15.) Find the mass of each of these objects whose weight on Earth is:
       a) 50 N        b) 80.O N        c) 0.98 N   H

16.) A ten kilogram mass lays on a desk. What force does the desk exert on the object?   S

17.) A person of mass 81.4 kg throws a 2.15 kg ball with a force of 20.8 N, west.
       Find the acceleration of both ball and person ignoring friction.   S

18.) If Joe, who weighs 625 N, stands on a bathroom scale calibrated in Newtons.
       a) What force would the scale exert on Joe?
       b) If Joe holds a 50 N cat in his arms, what force would the scale exert on Joe?
       c) After Joe puts down the cat, his father comes up behind him and lifts upward
          on his elbows with a 72 N force. What force would the scale now exert on Joe?   S

19.) A horizontal force of 16.1 N, east pulls a 52 N sled across the snow at a constant velocity.
       What is the coefficient of sliding friction between the snow and the runners on the sled?  S

20.) If a 650 N person sat in the sled in #19, what force would be
       needed to pull it across the snow at a constant velocity?  S

21.) The coefficient of sliding friction between rubber tires and wet pavement is 0.50.
       The brakes are applied to a 750 kg car traveling west and it skids to a stop.
       Find the force of friction the road exerts on the car.   S

22.) The coefficient of sliding friction between rubber tires and dry pavement is 0.80.
       The brakes are applied to a 1180 kg car traveling north and it skids to a stop.
       a) Find the force of friction the road exerts on the car.  S
       b) Find the acceleration of the car. Would it be constant?  S

23.) You are driving a 2500.0 kg car at a constant velocity of 14.0 m/s, east along an icy but
       straight and level road. You lock up the brakes and the car slides to a stop in 25.0 m.
       What is the coefficient of sliding friction between your tires and the icy road?  S

24.) A 0.21 g spider climbs up her web at a constant velocity.
       What force does the web exert on the spider?   S

25.) A 0.21 g spider climbs down her web at a constant velocity.
       What force does the web exert on the spider?   S

26.) A 4235 kg helicopter ascends at a constant velocity.
       a) What force does the air exert on the propellers?   S
       b) What force would the air exert on the propellers if it was descending?   S

27.) A 56.8 kg firefighter travels down a pole at a constant velocity with a 4.5 kg cat in one hand.
       What force does the pole exert on the firefighter?   S

28.) A 4500 kg helicopter accelerates upward at 2.0 m/s2.
       What lift force is exerted by the air on the propellers?   S

29.) The maximum force a grocery sack can withstand and not rip is 250 N.
        If 20 kg of groceries are lifted from the floor the table with an
        acceleration of 5.0 m/s2, will the sack hold?   S

30.) A student stands on a bathroom scale in an elevator at rest on the
        64th floor of a building. The scale reads 836 N.

        a) As the elevator moves up, the scale reading increases to 935 N, then
            decreases back to 836 N. Find the acceleration of the elevator.   S

        b) As the elevator approaches the 74th floor, the scale reading drops
            as low as 782 N. What is the acceleration of the elevator?   S

31.) Safety engineers estimate that an elevator can hold 20 persons
       of 75 kg average mass. The elevator itself has a mass of 500 kg.
       Tensile strength tests show that the cable supporting the elevator
       can tolerate a maximum force of 2.96 x 104 N. Calculate the greatest
       acceleration that the elevator can have without breaking the cable.   S

Answers