Tuesday
July 22, 2014

Homework Help: physics

Posted by lawrence on Wednesday, October 12, 2011 at 11:59am.

( 1.) An objectis thrown upward from the edge of a tall building with a velocity of 10m/s. Where will the object be 3s after it is thrown? Take g = 10m/s^2
15m above the top of the building
30m below the top of the building
15m below the top of the building
30m above the building

( 2.) A stone thrown from ground level returns to the same level 4s after. With what speed was the stone thrown? Take g = 10m/s^2
20m/s
10m/s
30m/s
15m/s

( 3.) What is common to the variation in the range and the height of a projectile?
horizontal velocity
time of flight
vertical velocity
horizontal acceleration

( 4.) A cart is moving horizontally along a straight line with constant speed of 30m/s. A projectile is fired from the moving cart in such a way that it it will return to the cart after the cart has moved 80m. At what speed (relative to the cart) and at what angle (to the horizontal) must the projectile be fired?
35.8m/s at 24degrees
38.6m/s at 54degrees
27m/s at 35degrees
24m/s at 44degrees

( 5.) The trajectory of a projectile is
an ellipse
a circle
a parabola
a straight line

( 6.) How fast must a ball be rolled along the surface of a 70-cm high table so that when it rolls off the edge it will strike the floor at the same distance (70cm) from the point directly below the edge of the table?
174.5cm/s
185.2cm/s
215.3cm/s
143.7cm/s

( 7.) A ball is kicked and flies from point P to Q following a parabolic path in which the highest point reached is T. The acceleration of the ball is
zero at T
greatest at P
greatest at T and Q
the same at P as at Q and T.

( 8.) A mass accelerates uniformly when the resultant force acting on it
is zero
is constant but not zero
increases uniformly with respect to time
is proportional to the displacement of the mass from a fixed point

( 9.) The term that best describes the need to hold the butt of a riffle firmly against the shoulder when firing to minimise impact on the shoulder is
forward displacement
forward acceleration
recoil velocity
pressure

( 10.) Two trolleys X and Y with momenta 20 Ns and 12 Ns respectively travel along a straight line in opposite directions before collision. After collision the directions of motion of both trolleys are reversed and the magnitude of the momentum of X is 2 Ns. What is the magnitude of the corresponding momentum of Y?
6 Ns
8 Ns
10 Ns
30 Ns

( 11.) A force of 2i + 7j N acts on a body of mass 5kg for 10 seconds. The body was initially moving with constant velocity of i 2j m/s. Find the velocity of the body in m/s, in vector form.
5i 12j
12i 5j
10i 7j
7i 10j.

( 12.) The exhaust gas of a rocket is expelled at the rate of 1300kg/s, at the velocity of 50,000m/s. Find the thrust on the rocket in newtons
6.7 x 10^7
3.5 x 10^7
7.6 x 10^7
5.7 x 10^7

( 13.) Sand drops at the rate of 2000kg/min. from the bottom of a hopper onto a belt conveyor moving horizontally at 250m/min. Determine the force needed to drive the conveyor, neglecting friction.
500N
800N
139N
152N

( 14.) A 30,000-kg truck travelling at 10.0m/s collides with a 1700-kg car travelling at 25m/s in the opposite direction. If they stick together after the collision, how fast and in what direction will they be moving?
8.1m/s
12.3m/s
24.2m/s
17.6m/s

( 15.) A gun of mass M is used to fire a bullet of mass m. The exit velocity of the bullet is v. Find the recoil velocity of the gun
Mv/m
mv/M
Mv/m
mv/M

( 16.) A 40-g ball travelling to the right at 30cm/s collides head on with an 80-g ball that is at rest. If the collision is perfectly elastic, find the velocity of each ball after collision

the first ball is going to the right at 10m/s while the other is going to the left at 20m/s

the first ball is going to the left at 10m/s while the other is going to the right at 20m/s

the first ball is going to the left at 20m/s while the other is going to the right at 10m/s

the first ball is going to the right at 10m/s while the other is going to the left at 10m/s

( 17.) A 10-g pellet of unknown speed is shot into a 2000-kg block of wood suspended from the ceiling by a cord. The pellet hits the block and becomes lodged in it. After the collision, the block and the pellet swing to a height 30cm above the original position. What was the speed of the pellet? (This device is called the ballistic pendulum)
480m/s
640m/s
350m/s
700m/s

( 18.) How large an average force is required to stop a 1400-kg car in 5.0s if the cars initial speed is 25m/s
2000N
3500N
9000N
7000N

( 19.) Which of these is not a statement of Newtons law of universal gravitation?

gravitational force between two particles is attractive as well as repulsive

gravitational force acts along the line joining the two particles

gravitational force is directly proportional to the product of the masses of the particles

gravitational force is inversely proportional to the square of the distance of the particles apart

( 20.) What is the gravitational field strength at a height h above the surface of the Earth?
gR^2/(R+h)^2
gR/(R+h)
g(R-h)/R
g(R-h)^2/R^2

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