PHYS 221 SI Worksheet

1. A car is rounding a flat, unbanked curve with radius, r = 230 m. If µk = 0.76 and µs = 0.96, what is the maximum velocity, vmax at which the driver can take the curve without skidding?

2. A farmer hitches his tractor to a sled loaded with firewood and pulls it a distance of 20 m along level ground. The total weight of the sled and load is 14,000 N. The tractor exerts a constant, 5000-N force at an angle of 36.9° above the horizontal and µk = 0.25. (a) Find the work done by each force acting on the sled and the total work done by all forces. (b) If the sled starts from rest, what is its velocity after being pulled 20 m? (c) How long does this 20-m trip take?

3. A block is placed near the edge of a horizontal turntable of radius 5 m that is initially at rest. It is attached to a motor that gives it an angular acceleration α. The coefficient of static friction between the block and the turntable is μs = 0.2. What is the maximum magnitude of the angular acceleration, α, that the motor can deliver so that the block will not slide the instant after the turntable begins to move?