Squid use jet propulsion for rapid escapes. A squid pulls water into its body and then rapidly ejects the water backward to propel itself forward. A 1.5 kg squid (not including water mass) can accelerate at $20 \mathrm { m } / \mathrm { s } ^ { 2 }$ by ejecting 0.15 kg of water. a. What is the magnitude of the thrust force on the squid? b. What is the magnitude of the force on the water being ejected? c. What acceleration is experienced by the water?

A girl stands on a sofa. Identify all the action/reaction pairs of forces between the girl and the sofa.

two children fight over a 200 g stuffed bear. The 25 kg boy left with a 17 N force. Ignore all other forces on the bear (such as its weight). a. At this instant, can you say what the velocity of the bear is? If so, what are the magnitude and direction of the velocity? b. At this instant, can you say what the acceleration of the bear is? if so what are the magnitude and direction of the acceleration?

A car is skidding to a stop on a level stretch of road. Identify all the action/reaction pairs of forces between the car and the road surface. Then draw a free-body diagram for the car.

Three ice skaters, numbered 1,2, and 3, stand in a line, each with her hands on the shoulders of the skater in front. Skater 3, at the rear, pushes on skater 2. Identify all the action/reaction pairs of forces between the three skaters. Draw a free-body diagram for skater 2, in the middle. Assume the ice is frictionless.

A car has a mass if 1500 kg. If the driver applies the brakes while on a gravel road, the maximum friction force that the tires can provide without skidding is about 7000 N. If the car us moving at 20 m/s, what is the shortest distance in which the car can stop safely?

What is the magnitude of the thrust force on the squid?

The light turns green and you accelerate rapidly forward so that you and your passenger feel "thrown back" into your seat. Consider your passenger to be the object.

The fastest pitched baseball was clocked at 46 m/s. If the pitcher exerted his force (assumed to be horizontal and constant) over a distance of 1.0 m, and a baseball has a mass of 145 g. a. Draw a free-body diagram of the ball during the pitch. b. What force did the pitcher exert on the ball during this record-setting pitch? c. Estimate the force in part b as a fraction of the pitcher's weight.

A $55 \mathrm{~kg}$ ice skater is gliding along at $3.5 \mathrm{~m} / \mathrm{s}$. Five seconds later her speed has dropped to $2.9 \mathrm{~m} / \mathrm{s}$. What is the magnitude of the kinetic friction acting on her skates?

The head injury criterion (HIC) is used to assess the likelihood BIO of head injuries arising from various types of collisions; an HIC greater than about $1000 \mathrm{~s}$ is likely to result in severe injuries or even death. The criterion can be written as $\mathrm{HIC}=\left(a_{\mathrm{avg}} / g\right)^{25} \Delta t$, where $a_{\text {avg }}$ is the average acceleration during the time $\Delta t$ that the head is being accelerated, and $g$ is the free-fall acceleration. as we discussed earlier shows a simplified graph of the net force on a crash dummy's $4.5 \mathrm{~kg}$ head as it hits the airbag during a automobile collision. What is the HIC in this collision?

Blocks with masses of 1.0 kg, 2.0 kg, and 3.0 kg are lined up in a row on a frictionless table. All three are puched forward by a 12 N force applied to the 1.0 kg block. How much force does the 2.0 kg block exert on (a) the 3.0 kg block and (b) the 1.0 kg block?

A constant force is applied to an object, causing the object to accelerate at $8.0 \mathrm { m } / \mathrm { s } ^ { 2 }$. What will the acceleration be if a. The force is doubled? b. The object's mass is doubled? c. The force and the object's mass are both doubled? d. The force is doubled and the object's mass is halved?

In t-ball, young players use a bat to hit a stationary ball off a stand. The 140 g ball has about the same mass as a baseball, but it is larger and softer. In one hit, the ball leaves the bat at 12 m/s after being in contact with the bat for 2.0 ms. Assume constant acceleration during the hit. a. What is the acceleration of the ball? b. What is the net force on the ball during the hit?