Physics test 2
A 2.5 -kg object experiences a single, time-dependent force Fx(t) =(18 N/s )t - (36 N ). What is the object's acceleration at t = 0? What is the object's acceleration at t = 2.0 s? What is the object's acceleration at t = 4.0 s?
-14.4 m/s^2, 0 m/s^2, 14.4 m/s^2
A(n) 1600-kg car going at 6.32 m/s in the positive x direction collides with a 3300-kg truck at rest. The collision is totally inelastic and takes place over an interval of 0.203 s. Assume that no brakes are applied during the collision and the car strikes the rear of the truck. Neglect the friction between the vehicles and the ground. A) What is the average x component of the acceleration of the car during the collision? B) What is the average x component of the acceleration of the truck during the collision? C) Are the ratio of accelerations and the ratio of inertias related the way you expect them to be? The inertias of the car and the truck are mc and mt respectively. X No, the ratio of the accelerations acx/atx is equal to −mt/mc, but it was expected to be −mc/mt. X Yes, the ratio of the accelerations acx/atx is equal to −mt/mc, as expected. X No, the ratio of the accelerations acx/atx is equal to −mc/mt, but it was expected to be mt/mc. X Yes, the ratio of the accelerations acx/atx is equal to −mc/mt, as expected.
-21 m/s^2 10 m/s^2 Yes, the ratio of the accelerations acx/atx is equal to −mt/mc, as expected.
When it crashes into a bridge support that does not move, a car goes from 115 km/h to 0 in 1.23 m. What is the impulse delivered to the 70-kg driver by the seat belt, assuming the belt makes the driver's motion identical to the car's motion? Assume that the initial direction of motion of the car is the positive direction. What is the average force exerted by the belt on the driver? If the driver were not wearing the seat belt and flew forward until he hit the steering wheel, which stopped him in 0.0145 s, what would be the average force exerted by the steering wheel on him?
-2240 N*s −2.90×10^4 N −1.54×10^5 N
The potential energy of an interaction is given by U(x)=ax2, where a = +6.4 J/m2. Initial speed of a 0.91-kg object in this system is 2.53 m/s at x = 0. How far does the object travel before it reaches a speed of v = 0? Does your answer in the previous part depend on whether the object is traveling in the positive or negative x direction? Yes, the answer in the previous part is for the object traveling in the negative x direction, the distance for the object traveling in the positive x direction is greater than the obtained result. No, it does not depend on whether the object is traveling in the positive or negative x direction. Yes, the answer in the previous part is for the object traveling in the positive x direction, the distance for the object traveling in the negative x direction is greater than the obtained result.
.67 m; no
A beetle that has an inertia of 3.4 × 10−6 kg sits on the floor. It jumps by using its muscles to push against the floor and raise its center of mass. If its center of mass rises 0.75 mm while it is pushing against the floor and then continues to travel up to a height of 350 mm above the floor, what is the magnitude of the force exerted by the floor on the beetle? What is the beetle's acceleration during the motion?
1.55×10^−2 N, 4560 m/s^2
A 4.7-kg steel ball is dropped from a height of 23 m into a box of sand and sinks 0.40 m into the sand before stopping. How much energy is dissipated through the interaction with the sand?
1100 J
When a(n) 870-kg compact car accelerates from rest to 26 m/s , it consumes 0.0766 L of gasoline, and 1.0 L of gasoline contains approximately 3.2×107 J of energy. What is the efficiency of the car? (Kf/Esi=)
12%
A(n) 8.4-kg object is sliding across the ice at 2.34 m/s in the positive x direction. An internal explosion occurs, splitting the object into two equal chunks and adding 19 J of kinetic energy to system. The explosive separation takes place over a 0.16-s time interval. Assume that the one of the chunks after explosion moves in the positive x direction. The x component of the average acceleration of this chunk during the explosion is afrontx, the x component fo the average acceleration of the other chunk during the explosion is arearx. What are the x components of the average accelerations of the two chunks during the explosion?
13, -13 m/s^2
A resort uses a rope to pull a 53-kg skier up a 15∘ slope at constant speed for 125 m . Determine the tension in the rope if the snow is slick enough to allow you to ignore any frictional effects. How much work does the rope do on the skier?
130 N, 1.7×10^4 J
A 33-kg girl climbs a 18-m rope in 27 s. What is her average power?
216 W
A ring is attached at the center of the underside of a trampoline. A sneaky teenager crawls under the trampoline and uses the ring to pull the trampoline slowly down while his 79-kg mother is sleeping on it. When he releases the trampoline, she is launched upward. As she passes through the position at which she was before her son stretched the trampoline, her speed is 3.0 m/s . How much elastic potential energy did the son add to the trampoline by pulling it down? Assume the interaction is nondissipative.
360 J
In a baseball game, a batter hits the 0.150-kg ball straight back at the pitcher at 190 km/h . If the ball is traveling at 160 km/h just before it reaches the bat, what is the magnitude of the average force exerted by the bat on it if the collision lasts 4.0 ms ?
3650 N
Two springs are hooked together end to end. When a 6.0-kg brick is suspended from one end of the combination, the combination stretches 0.15 m beyond its relaxed length. What is the spring constant of the combination? If the top spring stretches 0.10 m, what is the spring constant of each spring?
392 N/m, ktop, kbottom = 590,1200 N/m
The engine in an imaginary sports car can provide constant power to the wheels over a range of speeds from 0 to 70 miles per hour (mph). At full power, the car can accelerate from zero to 28.0 mph in time 1.00 s . At full power, how long would it take for the car to accelerate from 0 to 56.0 mph? Neglect friction and air resistance. A more realistic car would cause the wheels to spin in a manner that would result in the ground pushing it forward with a constant force (in contrast to the constant power in Part A). If such a sports car went from zero to 28.0 mph in time 1.00 s , how long would it take to go from zero to 56.0 mph ?
4 s, 2 s
You push with a steady force of 19 N on a 46-kg desk fitted with casters (wheels that swivel) on its four feet. How long does it take you to move the desk 5.1 m across a warehouse floor?
4.97 s
A 65-kg ice skater stands facing a wall with his arms bent and then pushes away from the wall by straightening his arms. At the instant at which his fingers lose contact with the wall, his center of mass has moved 0.50 m , and at this instant he is traveling at 2.5 m/s . What is the average force exerted by the wall on him? What is the work done by the wall on him? What is the change in the kinetic energy of his center of mass?
410 N, 0 J, 200 J
A 65-kg student is in an elevator moving downward with constant velocity. He uses a bathroom scale to measure the upward force exerted on his feet. What force magnitude does the scale read when the elevator is traveling at constant velocity? What force magnitude does the scale read when the elevator slows to a stop with an acceleration of magnitude 2.0 m/s^2 ? What force magnitude does the scale read when the elevator starts downward again with an acceleration of magnitude 2.0 m/s^2 ?
637 N, 767 N, 507 N
You are climbing a rope straight up toward the ceiling. What is the magnitude of the force you must exert on the rope in order to accelerate upward at 1.6 m/s2 , assuming your inertia is 59 kg ? What is the direction of this force? If the maximum tension the rope can support is 1225 N, what is the maximum inertia the rope can support at this acceleration if the inertia of the rope is so small that the gravitational force exerted on the rope can be ignored?
673 N, downward, 107 kg
You throw a 0.52-kg target upward at 15 m/s. When it is at a height of 10 m above the launch position and moving downward, it is struck by a 0.338-kg arrow going 26 m/s upward. Assume the interaction is instantaneous. What is the velocity of the target and arrow immediately after the collision? What is the speed of the combination right before it strikes the ground?
7 m/s, 16 m/s
The tension in the cable attaching the platform to the building on the right is 720 N. 45deg | 30 deg | crate | | | What is the tension in the cable attaching the platform to the building on the left? What is the inertia of the platform?
880 N, 100 kg
The work done by a certain force is given by W(Δx)=aΔx+b(Δx)^3. Write an expression for the force as a function of Δx.
F(Δx) = a+3b(Δx)^2
A motor must lift a 1100-kg elevator cab. The cab's maximum occupant capacity is 400 kg, and its constant "cruising" speed is 1.5 m/s . The design criterion is that the cab must achieve this speed within 2.0 s at constant acceleration, beginning from rest. When the cab is carrying its maximum capacity, at what average rate must the motor deliver energy to get the cab up to cruising speed? At what constant rate must the motor supply energy as the fully loaded cab rises after attaining cruising speed?
Pav = 1.19×10^4 W Pav = 2.21×10^4 W
Spring B is stiffer than spring A. Which one has more energy stored in it if you compress both springs with the same force? Both springs have the same energy. Spring A has more energy. Spring B has more energy. Which one has more energy stored in it if you compress both springs the same displacement from their relaxed lengths? Both springs have the same energy. Spring B has more energy. Spring A has more energy.
Spring A has more energy; Spring B has more energy
What is the direction of the frictional force exerted on a coffee cup sitting on a stationary table? What is the direction of the frictional force exerted on a coffee cup being pulled to the right across a table? What is the direction of the frictional force exerted on a coffee cup sitting on a table while the table is dragged to the right and moves on a smooth horizontal surface without friction?
There is no frictional force being exerted on the cup. To the left. To the right.
A force F⃗ = Fxι^ + Fyj^ with Fx = 51 N and Fy = 17 N is exerted on a particle as the particle moves along the x axis from x = 1.0 m to x = -5.0 m. Determine the work done by the force on the particle. What is the angle between the force and the particle's displacement?
W = -310 J, θ = 160∘
3kg 2kg 1kg Floor Answer the following questions with reference to the eight forces defined as follows. F3 on 2, F2 on 3, F3 on 1, F1 on 3, F2 on 1, F1 on 2, F1 on floor, and Ffloor on 1. Assume the elevator is at rest. Rank the magnitude of the forces. L-->S Now, assume the elevator is moving upward at increasing speed. Rank the magnitude of the forces. L-->S
a) F1 on floor and Ffloor on 1; F1 on 2 and F2 on 1; F3 on 2 and F2 on 3; F3 on 1 and F1 on 3 b) F1 on floor and Ffloor on 1; F1 on 2 and F2 on 1; F3 on 2 and F2 on 3; F3 on 1 and F1 on 3
Time tH it takes the projectile to reach its maximum height. tR, the time at which the projectile hits the ground. H, the maximum height attained by the projectile. The total distance R (often called the range) traveled in the x direction; in other words, find where the projectile lands.
tH = v0sinθ/g tR = 2v0sinθ/g H(θ) = v0^2sinθ^2/2g R(θ) = (v0cosθ)⋅2(v0sinθ/g)
Find v0y, the vertical component of the velocity of the ball when the quarterback releases it. Find v0x, the initial horizontal component of velocity of the ball. Find the speed v0 with which the quarterback must throw the ball. Assuming that the quarterback throws the ball with speed v0, find the angle θ above the horizontal at which he should throw it.
v0y = 1/2 (gtc) v0x = vr + (D/tc) v0= sqrt [(vr+D/tc)^2+(gtc/2)^2] θ = atan(v0y/v0x)
You want to walk down your icy driveway without sliding. If the incline of the driveway is 17 ∘ from the horizontal, what must the minimum coefficient of static friction be between your shoes and the ice?
μ = 0.31
