1.
hball on boxer fist/glove if he hits it at that accele 8. A contestant in a winter with a rope over his
er sporting events pulls a 45 kg block of ice in the positive hori oulder across a frozen lake as
shown in the figure. Assume the ev across riction are us 0.1 and u 0.03. Draw FBD. (15 points)
a) Calculate the minimum force F he must exert to get the block sliding. 25° ) What is its the
acceleration once it starts to move if that force maintained?
Solution
8) a) for the object to start moving
F cos 25 > static friction
F cos 25 = u s N
F cos 25 = u s *(mg - F sin 25)
F ( cos 25+ u s sin 25 ) = u s mg
F ( cos 25 + 0.1 sin 25) = 0.1*45*9.8
F = 46.5 N
b) acceleration is the force continues
Net force = (46.5 cos 25 - 0.03*(45*9.8 - 46.5sin 25)
= 29.5 N
Acceleration = F/ m = 29.5 / 45 = 0.65 m/s2