## Thursday, 11 September 2014

### FORCE PROBLEMS AND SOLUTIONS

F=ma         FORCE = MASS x ACCELERATION
.
Remember, mass is in kg - - force in in N (newtons) - - acceleration is in m/s2

1.     How much force is needed to accelerate a 66 kg skier at 2 m/sec2?

2.     What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec2?

3.     What is the acceleration of a 50 kg object pushed with a force of 500 newtons?

4.     The mass of a large car is 1000 kg.  How much force would be required to accelerate the car at a rate of 3 m/sec2?

5.     A 50 kg skater pushed by a friend accelerates 5 m/sec2.  How much force did the friend apply?

6.     A force of 250 N is applied to an object that accelerates at a rate of 5 m/sec2.  What is the mass of the object?

7.     A bowling ball rolled with a force of 15 N accelerates at a rate of 3 m/sec2; a second ball rolled with the same force accelerates 4 m/sec2.  What are the masses of the two balls?

8.     If a 60 kg person on a 15 kg sled is pushed with a force of 300 N, what will be person’s
acceleration?

9.     A force of 20 N acts upon a 5 kg block.  Calculate the acceleration of the object.

10.  An object of mass 300 kg is observed to accelerate at the rate of 4 m/s2.  Calculate the force required to produce this acceleration.

11.  A 5 kg block is pulled across a table by a horizontal force of 40 N with a frictional force of 8 N opposing the motion.  Calculate the acceleration of the object.

12.  An object of mass 30 kg is in free fall in a vacuum where there is no air resistance. Determine the acceleration of the object.

13.  An object of mass 30 kg is falling in air and experiences a force due to air resistance of 50 newtons.
a.      Determine the net force acting on the object and
b.      calculate the acceleration of the object.

SOLUTIONS

1.f=ma   f= 66 x 2    f = 132 N

2.F= ma   f= 1000 x 9.8  f=9,800 n

3. F= ma   500 = 50(a)   a= 10 m/s2

4.  F= ma      f= 1000 x 3    f= 3000 N

5. F = ma     f= 50 x 5     f= 250 N

6.  F = ma     250N=(m)5      m= 50kg

7.  F= ma         15N= (m)3  m=5kg        15N = (m)4   m=3.75kg

8.     F=ma              300N=(60+15)(a)          a=4 m/s2

9.    F=ma            20N=5(a)       a=4 m/s2

10.   F=ma              F=300 x 4        f= 1200N

11.  F=ma              40N-8N=32N of force in a direction     32N=5(a)      a=6.4 m/s2

12.   Since it is in free fall and is falling due to the force of gravity.....the acceleration will
always be 9.8 m/s2

13. f=ma  f=30 x 9.8   f=294N    Net force is 294-50 = 244N

acceleration of the object.
F= ma            244N=30 (a)       a=8.13 m/s2