91影视

A rubber-wheeled $50kg$ cart rolls down a $15掳$ concrete incline. What is the cart鈥檚 acceleration if rolling friction is

(a) neglected and

(b) included?

A $4000$kg truck is parked on a $15掳$slope. How big is the friction force on the truck? The coefficient of static friction between the tires and the road is $0.90$.

A football coach sits on a sled while two of his players build their strength by dragging the sled across the field with ropes. The friction force on the sled is $1000N$, the players have equal pulls, and the angle between the two ropes is $20掳$. How hard must each player pull to drag the coach at a steady$2.0m/s$?

Kat, Matt, and Nat are arguing about why a physics book on a table doesn鈥檛 fall. According to Kat, 鈥淕ravity pulls down on it, but the table is in the way so it can鈥檛 fall.鈥� 鈥淣onsense,鈥� says Matt. 鈥淎n upward force simply overcomes the downward force to prevent it from falling.鈥� 鈥淏ut what about Newton鈥檚 first law?鈥� counters Nat. 鈥淚t鈥檚 not moving, so there can鈥檛 be any forces acting on it.鈥� None of the statements is exactly correct. Who comes closest, and how would you change his or her statement to make it correct?

A 1500 kg car skids to a halt on a wet road where ${渭}_k$$=0.50$. How fast was the car traveling if it leaves role="math" localid="1648126746388" $65m$-long skid marks?

A $50,000$kg locomotive is traveling at $10m/s$when its engine and brakes both fail. How far will the locomotive roll before it comes to a stop? Assume the track is level.

You and your friend Peter are putting new shingles on a roof pitched at 25掳. You鈥檙e sitting on the very top of the roof when Peter, who is at the edge of the roof directly below you, 5.0 m away, asks you for the box of nails. Rather than carry the 2.5 kg box of nails down to Peter, you decide to give the box a push and have it slide down to him. If the coefficient of kinetic friction between the box and the roof is 0.55, with what speed should you push the box to have it gently come to rest right at the edge of the roof?

An Airbus $A320$ jetliner has a takeoff mass of $75,000$ kg. It reaches its takeoff speed of $82m/s(180mph)$ in $35$s. What is the thrust of the engines? You can neglect air resistance but not rolling friction

A medium-sized jet has a $3.8m$diameter fuselage and a loaded mass of $85,000kg.$The drag on an airplane is primarily due to the cylindrical fuselage, and aerodynamic shaping gives it a drag coefficient of $0.37$. How much thrust must the jet鈥檚 engines provide to cruise at $230m/s$at an altitude where the air density is $1.0kg/m^3?$

A $75kg$skydiver can be modeled as a rectangular 鈥渂ox鈥� with dimensions $20cm*40cm*180cm.$What is his terminal speed if he falls feet first? Use $0.8$for the drag coefficient.