Question

A 3 kg block is on a horizontal fricyioless plane. The tension in the string is 10 N. How much work is done on the block in moving it 20m? Starting from rest what is the final speed?

From problem 1, the coefficient of friction between block and the plane is 0.3. What is the net work done and the final speed?

from problem 1, if the coefficient is kinetic friction between the blockand the plane is 0.3 and the initial speed is 2 m/s, what is the net work done and final speed?

Answer 1

Work done, W= force*displacement

W= 10*20 = 200 J

u=0 m/s; acceleration,a= 10/3 m/s²; s= 20 m

v² - u² =2as

v= sqrt(2as)= sqrt(2*10*20/3)

v=11.547 m/s

Net force, F= T - mg = 10 - 0.3*3*9.81

F = 1.171 N

Work done, W= Force*displacement = 1.171*20

W=23.42 J

u=0 m/s; acceleration,a= 1.171/3 = 0.3903 m/s²; s= 20 m

v² - u² =2as

v= sqrt(2as)= sqrt(2*0.3903*20)

v=3.9512 m/s

Work done will remain same, W= 23.42 J

u=2 m/s; acceleration,a= 1.171/3 = 0.3903 m/s²; s= 20 m

v² - u² =2as

v= sqrt(2²+2as)= sqrt(4 + (2*0.3903*20))

v=4.4285 m/s