A 56-kg person stands in the middle of a raft which is at rest on a lake. If the person walks at constant velocity along the raft, the raft moves at a speed of 0.20 m/s relative to the ground. What is the speed of the person relative to the ground if the mass of the raft is 120 kg?

During a car collision, the knee, thighbone, and hip can sustain a force no greater than 4000 NN. Forces that exceed this amount could cause dislocations or fractures. Assume that in a collision a knee stops when it hits the car's dashboard. Also assume that the mass of the body parts stopped by the knee is about 20% of the total body mass. The person with a mass of 90 kgkg is initially traveling at 18 m/sm/s (40 mi/hmi/h).  What minimum stopping time interval in needed to avoid injury to the knee?  What is the minimum stopping distance?

Our brave astronaut Ms. Rose Noneck is at rest spacewalking 9.3 m away from her spaceship when her jetpack runs out of electricity (powered by TCC?). And worst – she is down to 60 seconds of oxygen left – there's plenty in her spaceship as well as her delicious lunch of baba ganoush. She remembers Prof. P's class and throws her 23.6 kg jetpack in the opposite direction of her spaceship at 1.4 m/s. Her mass is 55 kg. Will she make it back to her spaceship before she runs out of air? Convince me with numbers - tell me how long in seconds it takes for her to get back. Will we be seeing her in Exam 4? Or is it the end for her?

Particle A has mass m and moves directly to the right with speed v > 0. Particle B has one fourth the mass of Particle A and moves directly to the right with twice the speed of Particle A. Which of the following statements are true? (Pick two.) Particle A has greater momentum than Particle B. Particle B has greater momentum than Particle A. Both particles have the same momentum. Particle A has greater kinetic energy than Particle B. Particle B has greater kinetic energy than Particle A. Both particles have the same kinetic energy.

When the mass of an object moving at a constant speed doubles, its momentum changes by a factor of _______, and its kinetic energy changes by a factor of _______.

A 66.0-kg athlete leaps straight up into the air from a trampoline with an initial speed of 7.5 m/s. The goal of this problem is to find the maximum height she attains and her speed at half maximum height. (a) What are the interacting objects and how do they interact? This answer has not been graded yet. (b) Select the height at which the athlete's speed is 7.5 m/s as  y = 0.  What is her kinetic energy at this point? JWhat is the gravitational potential energy associated with the athlete? J(c) What is her kinetic energy at maximum height? JWhat is the gravitational potential energy associated with the athlete? J(d) Write a general equation for energy conservation in this case and solve for the maximum height. Substitute and obtain a numerical answer. m(e) Write the general equation for energy conservation and solve for the velocity at half the maximum height. Substitute and obtain a numerical answer. m/s

this is a practice problem, not a graded assignment

Two balls are about to collide. Ball 1 has a mass of 10kg, and is moving [down] at an unknown speed. Ball 2 is 11kg and is moving [up] at a speed of 6m/s. After they collide, ball 1 moves with a velocity of 8m/s [60° Up of right]. Ball 2 moves with an unknown velocity [55° down of left]. An image has been added to help picture the situation. What is the initial velocity of ball 1? 260° 59 5.1m/s [down] 5.38m/s [down] O 6.34m/s [down] O 6.9m/s [down]

After a 70-kg person steps from a boat onto the shore, the boat moves away with a speed of 0.70 m/sm/s with respect to the shore. If the same person steps from the shore onto the boat, the person and the boat move away from the shore at a speed of 0.50 m/sm/s. Assume that the initial speed of the person with respect to the shore is the same in both cases and that the person is moving in a horizontal direction. A. Determine the mass of the boat. B. Determine the speed of the person.