Question

1) A child pushes under an angle of 30⁰ an object 2m on a horizontal floor at constant speed. If the force applied by the child is 20N what is the work done?

2) A 200kg car traveling at 5 m/s runs into the rear of a car that has a mass of 150 kg and travels with 10m/s What is the speed of the cars after the collision assumed perfectly inelastic?

Answer 1

1)

F = force applied = 20 N

d = displacement = 2 m

= angle between force and displacement = 30

Work done is given as

W = F d Cos

W = 20 x 2 Cos30 = 34.6 J

2)

m1 =- mass of first car = 200 kg

v1i = velocity of first car before collision = 5 m/s

m2 = mass of second car = 150 kg

v2i = velocity of second car before collision = 10 m/s

V = velocity of combination after collision

using conservation of momentum

m1 v1i + m2 v2i = (m1 + m2) V

200 x 5 + 150 x 10 = (200 + 150) V

V = 7.14 m/s