Question

starting at rest ,a 5 kg object is acted upon only one force as indicated in figure find total woek done

Answer 1

Answer

90J

Explanation

Given that,

Force1 =20N

Force2 = -10N

time1 = 2 sec

time2 = 1 sec

Formulas to use

1)

Workdone = force x distance

2)

Distance = (vo • t) +  1/2(a • t²)

3)

Force = mass x acceleration

PART1

20 = 5 * acceleration

acceleration = 20/5

                     = 4m/s²

distance1 = 0 + 1/2(4 x 2²)

               = 1/2(4x4)

               = 1/2(16)

               = 8m

Workdone1 = 20 x 8

                  = 160

PART2

-10 = 5 * acceleration

acceleration = -10/5

                    = -2 m/s

v²-u² = 2as

v = √2(4)(8)

  = 8m/s

distance2 = 8(1) + 1/2((-2) x 1²)

                = 8 -1

                = 7m

Workdone2 = -10 x 7

                   = -70

Total workdone = 160 -70

                          = 90J