According to a report on traumatic brain injury, the force that a professional boxer’s fist exerts on his opponent’s head is equivalent to being hit with a $5.9 \mathrm{kg}$ bowling ball traveling at $8.9 \mathrm{m} / \mathrm{s}$ that stops in $0.018 s$.Determine the average force that the fist exerts on the head.

About $80 \mathrm{g}$ of blood is pumped from a person’s heart into the aorta during each heartbeat. The blood starts at rest with respect to the body and has a speed of about $1.0 \mathrm{m} / \mathrm{s}$ in the aorta. If the pumping takes $0.17 \mathrm{s}$, what is the magnitude of the average force exerted by the heart on the blood?

A $100-g$ apple is falling from a tree. What is the impulse that Earth exerts on it during the first $0.50 \mathrm{s}$ of its fall? The next $0.50 \mathrm{s}$?

You decide to use your garden hose to wash your garage door. The water shoots out at a rate of $10 \mathrm{kg} / \mathrm{s}$ and a speed of $16 \mathrm{m} / \mathrm{s}$ with respect to the hose. When the water hits the garage, its speed decreases to zero. Determine the force that the water exerts on the wall. What assumptions did you make?

Certain natural forms of potassium have nuclei that are radioactive. Each radioactive potassium nucleus decays to a slightly less massive daughter nucleus and a high-speed electron called a beta particle. If af ter the decay the daughter nucleus is moving at speed $200 \mathrm{m} / \mathrm{s}$ with respect to the decaying material, how fast is the electron (the beta particle) moving? Indicate any assumptions you made. The mass of the daughter is about 70,000 times greater than the mass of the beta particle.

(a) What force is required to stop a 1500-kg car in a distance of 0.20 m if it is initially moving at 2.2 m/s? (b) What if the car is moving at 4.5 m/s?

Explain the factors that affect the rate of glomerular filtration and how this rate is regulated.

During a collision when an average stopping force F is exerted on a car by an obstacle, the car's bumper retracts a distance $\Delta x$. These two quantities are related by the equation $F \Delta x=0.5 m v_{0}^{2}$. Use proportional reasoning to determine (a) the necessary percent change in the retraction distance so that the average force required to stop a car is reduced by 20% and (b) the percent change in initial to final speed that would produce the same reduction in force.

The train tracks on which a train travels exert a $2.0 \times 10^{5} \mathrm{N}$ friction force on the train, causing it to stop in $50 \mathrm{s}$. (a) Determine the average force needed to stop the train in $25 \mathrm{s}$.(b) Determine the stopping time interval if the tracks exert a $1.0 \times 10^{5}-N$ friction force on the train.

Your friend is catching a falling basketball after it has passed through the basket. Her hands move straight down 0.20 m while catching the ball. Estimate (a) the time interval for the ball to stop as she catches it and (b) the average force that her hands exert on the ball while catching it. Indicate any assumptions or estimates you have to make in order to answer the questions.

A person in a car during a sudden stop can experience potentially serious chest injuries if the combined force exerted by the seat belt and shoulder strap exceeds $16,000 \mathrm{N}$. Describe what it would take to avoid injury by estimating (a) the minimum stopping time interval and (b) the corresponding stopping distance, assuming an initial speed of $16 \mathrm{m} / \mathrm{s}$. Indicate any other assumptions you made.

The same $100-g$apple is falling from the tree. What is the impulse that Earth exerts on it during the first $0.50 \mathrm{m}$ of its fall? The next $0.50 \mathrm{m} ?$

A cart of mass $m$ moving right collides with an identical cart moving right at half the speed. The carts stick together. What is their speed after the collision?

(a) A 145-g baseball travels at 35 m/s toward a baseball player’s bat (the bat is the object of reference) and rebounds in the opposite direction at 40 m/s. Determine the ball’s momentum change (magnitude and direction). (b) A golfer hits a 0.046-kg golf ball that launches from the grass at a speed of 50 m/s. Determine the ball’s change in momentum.