# A Few Tough Physics Problems! I'm stuck,

1. Sep 24, 2008

### tristan4040

1. Two canoeists in identical canoes exert the same effort paddling and hence maintain the same speed relative to the water. One paddles directly upstream (and moves upstream), whereas the other paddles directly downstream. With downstream as the positive direction, an observer on shore determines the velocities of the two canoes to be -1.2 m/s and +2.9 m/s, respectively.

(a) What is the speed of the water relative to shore?
m/s

(b) What is the speed of each canoe relative to the water? canoe going upstream m/s
canoe going downstream m/s

2. Two packing crates of masses m1 = 10.0 kg and m2 = 6.50 kg are connected by a light string that passes over a frictionless pulley as in Figure P4.26. The 6.50 kg crate lies on a smooth incline of angle 39.0°. Find the acceleration of the 6.50 kg crate.

a) m/s2 (up the incline)

b) Find the tension in the string.
N

3. When baseball outfielders throw the ball, they usually allow it to take one bounce on the theory that the ball arrives sooner this way. Suppose that after the bounce the ball rebounds at the same angle θ as it had when released but loses half its speed.

(a) Assuming the ball is always thrown with the same initial speed, at what angle θ should the ball be thrown in order to go the same distance D with one bounce as one thrown upward at ϕ = 48.2° with no bounce?
°

(b) Determine the ratio of the times for the one-bounce and no-bounce throws.
t1b / t0b =

4. A dart gun is fired while being held horizontally at a height of 0.90 m above ground level and while it is at rest relative to the ground. The dart from the gun travels a horizontal distance of 4.00 m. A college student holds the same gun in a horizontal position while sliding down a 45.0° incline at a constant speed of 2.00 m/s. How far will the dart travel if the student fires the gun when it is 1.00 m above the ground?

m

5. A 4.9 g bullet leaves the muzzle of a rifle with a speed of 332 m/s. What force (assumed constant) is exerted on the bullet while it is traveling down the 0.85 m long barrel of the rifle?
N

2. Sep 24, 2008