Physics 11 (Fall 2010) Midterm Review Questions Q1) A block initially at rest is allowed to slide down a frictionless ramp and attains a speed v at the bottom. To achieve a speed 2v at the bottom, how many times as high must a new ramp be?

Q2) An object is held in place by friction on an inclined surface. The angle of the incline is increased until the object starts moving. If the incline is kept at this angle, what happens to the object?

Q3) When is the normal force on an object equal to its weight?

Q4) At the bowling alley, the ball-feeder mechanism must exert a force to push the bowling ball up a 1.0 m ramp. The ramp leads the balls to a chute 0.5 m above the base of the ramp. Assuming that ball starts and ends at rest, approximately how much force must be exerted on a 5.0 kg bowling ball?

Q5) Can an object have zero velocity and nonzero acceleration simultaneously? Can an object have zero acceleration and nonzero velocity simultaneously?

Midterm Review Problems P1) The speed limit in a school zone is 25 mph. A driver traveling at this speed sees a child run into the road 13 m ahead of his car. He applies the brakes and the car slows down at a constant rate of 8.0 m/s2. If the driver’s reaction time is 0.25 s, will the car stop before hitting the child? (Answer: Yes – the car drives x = 11 m before stopping.) P2) A ball with a mass of 0.15 kg is connected to a rope of length 1.50 m. The ball is released from rest from a height of 0.35 m as shown in the figure. What is the tension in the rope at the lowest point? (Answer: T = 2.2 N)

h = 0.35m

P3) A ball is thrown from the top of a 31.0 m tall building. The ball is thrown with an initial speed of 14.0 m/s at an angle of 35o. What is the speed of the ball right before it hits the ground? (Answer: v = 28.3 m/s) P4) A 3.0-kg block starts at a height h = 60 cm on a plane that is frictionless and has an inclination of 30o. Upon reaching the bottom, the block slides along a rough horizontal surface with coefficient of kinetic friction μ k = 0.25 . How far does the block slide on the horizontal surface before coming to rest? (Answer: x = 2.4 m) P5) A very small dog (M = 4.5 kg) leaps straight up and catches a Frisbee (m = 0.50 kg) at the high point of the jump. The velocity of the dog and Frisbee immediately after the catch is 0.60 m/s to the right. What was the velocity of the Frisbee just before being caught? (Answer: v = 6.0 m/s) P6) A vertically moving projectile reaches a maximum height of 23 m above its starting position. a) What was the projectile’s initial speed? (Answer: 21 m/s) b) How fast is the projectile moving when it is 11.5 m above its starting point? (Answer: v = 15 m/s) P7) A 5.0-kg block is set into motion up an inclined plane (30o) with an initial speed of 8.0 m/s. The block comes to rest after traveling 3.0 m along the plane. What is the coefficient of kinetic friction? (Answer: uk = 0.68) v0 = 8 m / s

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