4 (c) 3.4, 4.8 ms (d) 3.4, 6.8 ms? A box of mass 25 kg starts from rest and slides down an inclined plane 8 metre long and 5 metre high. It is found to move at the bottom at 7 m/s. What is the force of friction? (a) 79.6 N (b) 96.6 N (c) 76.6 N (d) 116.6 N (c) 50 m/s (d) 10 m/s A bullet having a speed of 100 m/sec crashes through a plank of wood. After passing through a plank, its speed is 80 m/s. Another bullet of the same mass and size, but traveling at 80 m/s, is fired at the plank. The speed of the second bullet after traveling through the plank is (Assume that resistance of the plank is independent of the speed of the bullet): -.1 Linental tound with some E 1